I'm aiming for scoring 4.5 in the GRE analytical writing session.

'For scoring' would be used with a way of doing something not an actual target which is the 4.5 in this case.

Please make a judgement of my essay and teach me how to revise itreview my essay and give feedback if needed.

Whilst not wrong, 'judgment' and 'teach' are 2 rather formal words for an informal request like this. The above is a simpler way of asking for feedback.

The assessment of a great person is not a trivial onetask.

Whilst it is correct, someone may ask ...a trivial what? You could also say ...is not to be taken lightly.

The prompt suggests that people's greatness can be decided only by those who live after them and .....I mostly agree with theat idea for three reasons.

There may be many ideas as to how it can be decided but using 'that' specifically identifies the idea mentioned.

It is after the person's death when he or she will have no more direct influence on society.

It isn't wrong as such but including 'after' highlights a point in the person's life not the actual death itself.

Hence, no one can make a complete judgment until he or sheafter the person dies.

Including 'after' shows that a judgment can be done at any time after their death not on their death. Also using 'the person' instead of 'he or she' flows a little smoother.

For instance, Yang Jian, an emperor of the Sui dynasty, had donedid multiple great works during his youth.

A native speaker would not use 'had done'.

He constructed the Great Canal and eliminate thed starvation in China.

Probably just a typo on 'eliminate' but it is in the past tense so should be eliminated. Also there is no article 'the' for starvation as it is a general statement. You would include 'the' if saying for example...'He eliminated the starvation caused by poor rice crops'.

Many insurgencies broke out during his later years.

Later is better used when talking about a period of time and not specific points in time such as; he was late for his appointment.

Therefore, Yang Jian eventually leftnded up with a bad reputation in China'sese history, despite the greatness inof his early life.

A native speaker would tend to use the above as it flows a little more smoothly.

Second, a person's reputation can affect the person itselfthemselves.

It is a living person not an inanimate thing.

If a person enjoys a wonderful reputation, he or she may consequently become complacent, which can harms his or her personality.

You don't need 'consequently' as it is implied in the remainder of your sentence.

On the other hand, a too good reputation can laterearly on can cause negative assessments later on.

This flows a little better.

For instance, Chen Kaige, a director famous for his very first movie, has never produced a movie comparable with his first and greatest one.

Didn't need had as the fact it is in the past is shown in the sentence.

Although his other movies aren't too bad, he suffers a bad reputation since people always keep abad as such, his reputation suffers as people have high expectations of him.

Saying 'aren't too bad' implies that they are bad at some level but this may not be the case, just not as good as his first.

Therefore, we cannot too focus too much on the temporary reputation of onea person, especially when it's a good one.

Minor issue on word order at the beginning.

Moreover, contemporaries may be shortsighted, as they cannot foresee the long-term influences of a person.

It flows a little better this way and there can be more than one influence.

For instance, Thea doctor who invented an operation, in which he cut offut a part of thea patient's brain, was reawarded a Nobel prize.

It is not a specific doctor in this context so 'a' instead of 'the. Out is used in this context. Also, whilst there is a money attached to a Nobel prize (the reward), the prize itself is awarded (given).

Since his contemporaries believed this canould cure any mental disease.

A mixture of present tense talking about the past.

However, people later realized that such an operation often wipes out a person's personality.

You could also say 'can often wipe out'

ThereforeAs a result, he getis enormously negative judgment nowadays longer considered a pioneer of brain surgery.

Yours is not wrong but a native speaker would probably say it this way

A person mustshould listen to other's assessments to be aware of his or her disadvantageshortcomings.

I presume you mean a person should always try to identify their own faults from others view of them.

In conclusion, a person's greatness can be better judged by people who live after themthose left behind when someone dies.

Your sentence is correct but could be someone 3000 years in the future for example. The sentence above means it is more likely to be those who are in the recent past.

Since not evAs a perysone can keep his or 's reputation can change during their greatness till death, a person's good reputation may rather end in a bad reputation, andlifetime, a once good reputation may end up bad later in life. So contemporaries cannot really foresee the long-term influences ofn a person's character.

Whilst your answer isn't wrong, a native speaker would tend to say it as above. In the last sentence, you are highlighting the fact that contemporaries can't predict what may change a person's character as they age.

However, we shouldn't overlook contemporaries' opinions tooas well.

Your sentence is not wrong but 'too' can often mean ‘excessively’ as in 'too much' or 'too many'. A native speaker would probably not use it in this context