Nothing is wrong with your grammar, but there are a few minor errors. It's important to remember that in written English there are always spaces after puntuation.

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Original:

May 12 is Mothers' Day in China.Hm,..Well, at this moment, I am for away from my family because I study in another province for my college study.And I miss my family very much.So,to conclude, Mama,I love you!Enjoy your day! PS: I also took a pic for you, mom!Love you.

Correct:

May 12 is Mothers' Day in China. Hm,.. Well, at this moment, I am for far away from my family because I study in another province for my college study. And I miss my family very much. So, to conclude, Mama, I love you! Enjoy your day! PS: I also took a pic for you, mom! Love you.

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Also, it's best to write ... not ,..

These are all very small errors, though; they don't interfere with the meaning of the entry. Without the corrections, everything still makes sense. Well done!