with greencard, to work in China

Hi,

I have got greencard for 2 years, want to keep greencard status and apply for citizenship after another 3 years.

Now I have a chance to work in China, I heard that there are some requirements for citizenship application, such as to stay in US for 2.5 years within 5 years, and can not leave from US for 0.5 years.

But how about greencard status? I was told there is possibility that border officer could revoke my greencard if he/she thinks I donot intend to stay in US as PR.

Any details comments? thanks much for the help

gcfighter