I dwon't give any synopsis here because everything in this article is as unpredictable as same as my uncertain life.

At that time, anyone who wanted to go into SZ downtown SZ would have preparedhad to get a special pass card which was approved by the local government.

My two older sisters saw me off at the railway station,. I forget my feelings then / forget how I felt then.

On the contrary, I remembered how excited they were when they came to greet me at the same place several months later when I came back to see them from SZ, I was too moved even to speak.

Nicely written.

What I havehad I experienced in such a changeable, unfamiliar, lively and energetic young city?

“What had I experienced” means “what had I experienced during my first several months in SZ, up to the moment described in the previous sentence. This is correct if the remainder of this post describes just those first several months.

My first destination was a toy factory, a ventured established and run by Hongkong people.

My mother's friend recommended her daughter host me.

I assume that “host me” means you stayed (lived) at her home.

He introduced me to his boss askingnd asked for a job for me.

The Hongkonger let me doserve as a worker aton the assembly line, t. This factory mainly manufactured ornaments for Christmas.

My colleagues said I would be promoted if I worked well because I looked like haved got a good education.

I dwon't give any synopsis here because everything in this article is as unpredictable as same as my uncertainmy eventful life.

You have not began telling your story from the time point of this sentence, so use future tense: you will (or will not) give a synopsis
To structure 'as': "as (adjective) as (noun you're comparing with)"
"Uncertain life" implies you feel doubtful about your life choices. If a lot of unpredictable things happen in your life, you can say "eventful life"

At that time, anyone who wanted to go intoenter SZ downtown would have prepared a special pass card which was approved by the local government.

'enter' is more natural than 'go into'

My two older sisters saw me off at the railway station,. I forgeot myhow I feelingst back thean.

You have already forgotten by the time you're speaking of this, so past tense "I forgot"
"I forgot my feelings back then" would work, but it's a bit hard to understand (do you mean that at the moment, you decided to wipe your head clean of your feelings to start anew, or have you forgotten the emotions you felt back then?), so you can disambiguate it by saying "how I felt back then"

On the contrary, I remembered how excited they were when they came to greet me at the same place several months later, when I came back from SZ to see them from SZ,. I was too moved even to speak.

You are remembering it right now to recount it to us-- use present tense "I remember"

What I have I experienced in such a changeablen ever-changing, unfamiliar, lively and energetic young city?

When you structure a sentence, usually you swap the order of subject and verb.
"What have I experienced?" "What did you see?"
"changeable" is not a very common word, so if you want to say that SZ changes a lot, use "ever-changing" -- it is always changing

My first destination was a toy factory ventured by(owned/ funded ?) by people from Hongk Kong people.

You wouldn't say "China people," so you should say"people from Hong Kong"
"Venture" is a term in the field of business, but as a noun, not a verb.

My mother's friend recommended that her daughter should host me.

When you connect "recommend" with a clause, use conjunction: "recommend that (action)"

He introduced me to his boss asking for a job for mend asked him to give me a job.

This structure is grammatically correct, but is a bit confusing to read and repeats "for" twice in close conjunction

The Hongkonger let me dowork as a worker at the assembly line, t. This was a factory that mainly manufactured ornaments for Christmas.

Person from Hong Kong = "Hong Konger"
"This factory mainly manufactured ornaments" works, but this structure is a bit simple and generic, so you can change it up a bit with "This was a factory that mainly manufactured..."

My work card was printed asI was assigned a Staff Card, and most of the other workers' were printed aswere assigned with Worker Cards.

"assign" means to formally give you something in a professional/ educational context, so it sounds quite natural here

My colleagues said I would be promoted if I worked well because I looked like have gotI had a good education.

Starting from today, I'll be writing a new series that describes my first-year experience in SZ (Shenzhen, a special economic zone in China).

I dwon't give any synopsis here because everything in this article is unpredictable asin the same way as my uncertain life is.

At that time, anyone who wanted to go into SZ's downtown would have prepared a special pass card which was approved by the local government.

My two older sisters saw me off at the railway station,. I forget myhave forgotten the feelings I had then.

On the contrary, I remembered how excited they were when they came to greet me at the same place several months later when I came back to see them from SZ,. I was too moved to even to speak.

This is a very sweet sentence.

What I have I experienced in such a changeable, unfamiliar, lively and energetic young city?

Remember, the verb comes directly after a question word like what, where, who, when, and how.

My first destination was a toy factory ventured byfinanced by people from Hongk Kong people.

My mother's friend recommended her daughter to host me.

He introduced me to his boss to asking for a job for me.

The Hongk Kong let me do as a worker atowners let me work on the assembly line, t. This factory mainly manufactured ornaments for Christmas.

My work card was printed as a Staff Card, and most of the other workers' were printed as Worker Cards.

My colleagues said I would be promoted if I worked well because I looked like have gotas if I had received a good education.

I don'twill give any synopsis hereno summary because everything in this article is unpredictable as same as, like my uncertain life.

I don't undestand the register you want to use as you bounce between a rather sophisticated one and a simpler one.
"Synopsis" is quite formal and I've barely even heard of it.
A more natural costruction could be "... because I want everything in this article to be unpredictable..."

I took a small bag and went to SZ.

"I went to SZ carrying only a small bag" may be better

At thate time, anyone who wanted to go into SZthe downtown would have preparedhad to have a special pass card which was approved by the local government.

"had to" indicates that that there was an obligation, and therefore the pass card was not only the best practice

My two older sisters saw me off at the railway station, I forget my feelings thenI had no recollection of my feelings after my two older sisters had seen me off.

I feel this is more natural; if you want to keep your construction, "afterwards" would probably be better than "then"

On the contraryother hand, I remembered how excited they were when they came to grseet me (at the same place) several months later, when I came back to see them from SZ, I was too moved I couldn't even to speak.

What I have I experienced in such a changeunstable, unfamiliar, lively and energetic young city?

My first destination was a toy factory ventured by Hongk Kong people.

I'm not that sure that "ventured" is the optimal expression, but it should be just fine

My mother's friend recommendedsuggested that her daughter could host me.

He introduced me to his boss, asking in my behalf for a job for me.

The Hongkong let me doin as a worker at the assembly line,; this factory mainly manufactured ornaments for ChristmaChristmas ornaments.

My work card was printed as a Staff Card, andwhereas most of the other workers' ones were printed as Worker Cards.

My colleagues said I would be promoted if I worked well because I looked like have gotI had a good education.

MOn the other hand, most of them were from the countryside.