".. we can't communicate very well because of my poor English". 
Really? 
What if you wrote this instead: 
" .. we can't communicate very well because of their poor Mandarin/Shanghaiese". 
Or, if you want to be more even-handed, then:
" .. we can't communicate very well because of the language barrier".

First notebook entry: Introducing myself

I am Renee Liu. I live in mainland China, I work ( Worked is past tense, so if you still work in Shanghai you must use work!)  in Shanghai and live in Hefei which is 3.5 hours away from Shanghai by train. I go back to my home every weekend. It may be shortened to 2 hours after the World Expo.That's  good news for me.
I'm an office manager for Red Dot China, I take care of evrything in the Red Dot China office such as HR,sales support,import&export sales, supporting the office manager etc. When I work with my workmates in the U.S.A, we can't communicate very well because of my poor English, so I want improve my English Asap.
( You cant start a sentance in English with And) Also when I was in university, my major was ( 'is' is present tense, you are not in university now so you need to use past tense) Chinese Language and Literature, I 'd like to help someone who want to learn Chinese.

Dont forget to use a space after a full stop!!!!

Work in Shanghai,Live in Hefei

I am Renee Liu.I live in China mainland,I worked in Shanghai and live in Hefei which is 3.5 hours away from Shanghai by train.I go back to my home every weekend.It may be short to 2 hours after the World Expo.That's a good news for me.
I am office manager of Red Dot China,I take care of evrything in the Red Dot China office such as HR,sales support,import&export,sales support,office manage etc.When I work with my workmates in the US,we can't communicate very well because of my poor English,so I want improve my English Asap.
And also,when I was in university,my major is Chinese Language and Literature,I 'd like to help someone who want to learn Chinese.