Good chance

You will have good chance to apply for an H1B stamp
in China.
Make sure you bring all the necessary documents such
as I797, pay check stubs, employment letter, tax return,
W2 form, previous I-20, previous visa/passport photocopies.

However, there is always some risk for applying for
a visa.
Since you are applying for an H1B, you may have better
chance.
Good luck!