Ma Tao, onceAfter graduateding from Nankai University and worked at their university, Ma Tao transitioned to becoming an employee there.

This is good - correct usage of the word "once" to denote when an action is completed. While easily understandable to a native speaker, I just tried to make it sound more formal, we have this word "transition" meaning to move to a different (usually higher) level than previously.

Later on, he meets Liu Ning, hisa colleague of his, and gets married to her.

by saying "his colleague" this implies intimate acquaintance before already having met her.

And then, he and his wife quit their current jobs and returned to Ma's hometown Fuyang to become vegetable farmers because of the pressure ofharsh reality (His wife's parents got ill and needed a lot of money, but their salaries of beingas university teachers couldn't affordcover it).

So this is a story about how Ma Tao and his wife Liu Ning quit their jobs to become vegetable farmers.

Theis short English passage is only a small translationexcerpt from thea Chinese story, but I wi'll translate the whole story into English.

In my opinion this is essentially perfect, I just tried to introduce the word "excerpt" to give you a better sense of its usage.

Ma Tao, once graduated from Nankai University and worked at their university.

I don't think "once" here is strictly wrong, but it sounds weird, given that most people only graduate once anyway.

Later on, he meetst Liu Ning, his colleague, and getsot married to her.

Put into past tense. If it was intended to be present, it is correct, but sounds strange.

And then, he and his wife quit their current jobs and returned to Ma's hometown, Fuyang, to be vegetable farmers because of the pressure of reality (His wife's parents got ill and needed a lot of money, but their salaries of being university teachers couldn't afford it).

job -> jobs.

So this is a story about how Ma Tao and his wife Liu Ning quit their jobs to be vegetable farmers.

job -> jobs.