Finally, Shanghai welcomed this autumn, and my favorite flower in AutumnAutumn flower, osmanthus, has been blooming.

It sounds better to say Autumn flower. Also because osmanthus is a bit of extra information, we need a comma on both sides.
As a side note, you use the american spelling of "favorite", but you're using "autumn" instead of "fall". I haven't corrected it, but it's something to think about~

I can smell it when I open my window in the morning, and when I'm walking on the road.

Using present continuous is what i would say if i was speaking.

I love the sweet and joyful fragrance of osmanthus.

It's not necessarily wrong to use joyful, but it also doesn't sound particularly native in this context. Maybe something like "sparkling" would get the same idea across, and as a bonus it alliterates

In the past, I often bought some perfumes that claimed to smell like osmanthus.

"often" implies more than one time, so making perfume plural works better. You could also say "bottles of perfume". Using "some" without making perfume plural or specifying bottles makes it sound like you are talking about the liquid contents of a particular brand that you bought multiple times. From the next sentence, i assume this isn't your meaning.

But unfortunately, they were not somehow, somehow they did not, not even those that I thought it was the first timat first were accurate.

Finally,At last! Shanghai welcomed thise autumn, and my favorite flower in Autumn, osmanthus has been blooming season, which also brought in the blossoming of my favorite flower—the osmanthus.

I can smell its fragrance flow in when I open mythe window in the mornings, and when I walk on theor (surrounds me) when I'm simply walking down a road.

I so love the sweet and joyblissful fragrance of osmanthus.es,

I often bought someso much that I often buy perfume thats claimed to smell like osmanthusing its wonderful fragrance.

But unfortunately, they were not somehow, even those I thought it was theto my disappointment, they weren't (though I really thought they were at first time).

AnywayNevertheless, I reastilly enjoy these autumn days.

Finally, Shanghai welcomed this autumn, aautumn has arrived in Shanghai. And, my favorite flower in Autumn, osmanthus, has been blooming.

"Shanghai welcomed this autumn" is perfectly fine grammatically but doesn't sound natural.

I can smell it when I open my window in the morning, and when I walk on the road.

But unfortunately, somehow they were not somehow,n't reminiscent of osmanthus' fragrance. This happened with even those I thought it wasried for the first time.

I'm not 100% sure what you mean by "even those I thought it was the first time" so my replacement sentence is my best guess. I extended on your original work to add clarification so that the reader can follow more easily. Putting somehow upfront improves sentence flow.

Anyways, I really enjoy these autumn days.

Perfectly find grammatically using "these autumn days" but simply "autumn days" sounds more natural.