does anything special indeed to getting Z visa from the embassy ?

It doesn't need a special background like how many trip you made to China & with which type of visa. For work visa (Z visa) application, the key documents are the Alien Employment License and Invitation Letter of A Duly Authorized Unit, if your employer can send the two documents to you, it is greatly possible for you to get a Z visa to China.

thanks for replay ... .
did you know how much we must pay to embassy ... and what kind of the document embassy need ?
thanks in advanced .

It costs US$ 30 for single entry Z visa. The requirements are:
1. your passport with at least 15 months remaining validity and 2 blank visa pages
2. one passport photo
3. complete visa application forms V.2011A and V.2011B on computer
4. the alien employment license, your employer needs to get it for you
5. invitation letter of a duly authorized unit, your employer needs to get it for you
6. medical certificate