Have got the visa for One month entry for one time. so how should i get the working Z

To apply for a working Z type, you should first prepare those documents including your passport and copy of its data page, a completed application form, a recently-taken passport-style photo, alien employment permit and other require documents. Then, submit the application to the CVASC. The duration you can stay in China depends on the actual days you need. The consular officers will give you proper duration of stay.