A working Z visa is required for persons wanting to work in China.  It is also issued to aliens who come to China for commercial entertainment performance. It is only granted if you and the employer meet certain requirements.  First, the organization must be accredited to employ foreigners.  You must meet the requirements as a 'foreign expert' and the employer must obtain a certificate stating that you comply.  The most common employment is teaching English for which the minimum qualifications are stated as having English as a first language and having at least a Bachelors degree.  However, there is some flexibility in these requirements so if you can find a willing employer they still have a chance of obtaining approvals for you.
The employer will send you a government issued Employment Permit and Visa Notification Letter which you must submit with a photocopy with your application. 
The visa is valid for only 30 days from the date of arrival during which time you and your employer must seek a Temporary Residence Permit for the duration of your contract, to the minimum of 90 days and the maximum of 12 months.

Requirements

1. Applicant's valid actual passport with at least six months validity left before expiration and at least one blank page left in it.

2. One truly completed Visa Application Form and the Supplementary Visa Application Form. 

3. One recent passport standard photo affixed on the Application Form.

4. 'Invitation Letter of Duly Authorized Unit' or 'Confirmation Letter of Invitation'

5. Alien Employment License for Foreigners from the Ministry of Human Sesourse and Social Security of the PRC shall be provided

6. Work Permit (one of the following work permits):
  Foreign experts, scholars, teachers or managers to be working in Mainland of China  
should provide the Confirmation Letter for Foreign Experts from the State Administration of Foreign Experts Affairs of the PRC

Chief Representative of the permanent office of foreign enterprise in PRC should provide the Registration Certificate from the local Administration for Industry and Commerce
Foreigners engaged in offshore petroleum operations in PRC should provide an Invitation Letter issued by China National Offshore Oil Corporation;
Foreigners to be engaged in commercial entertainment performance in China should provide the temporary commercial entertainment performance permit from the Ministry of Culture of the PRC. If the band has not more than five members, only the Visa Notification from the Foreign Affairs Office of province, autonomous region or municipality is required.
Other foreigners who comes to china for employment should provide the Employment Certificate for Foreigners (Work Permit) issued by the Ministry of Labor and Social Security of the PRC
7. For the accompanying family members, they are not required to provide a Visa Notification Form or a Working Permit; they should provide Proof of Relative Relationship e.g. Marriage Certificate, Birth Certificate, etc

How to Apply
You can go to the Chinese embassy, consulates or other diplomatic missions in person for visa application. You can also entrust your friends, a travel agency or visa agency to act on your behalf. There is no need to make an appointment. Mailed applications are not acceptable.

Note:
1) To apply for the z visa, it is also required to provide Health Certificate.
2) The Health Certificate record for Foreigner filled out and signed by a doctor (together with their copies).Please take note that your Physical Examination Report (see the form) should used within 6 months since its issuing date.
3)  If you are in China to apply the 'Z' visa then it is required to provide Health Certificate issued by China Entry-Exit Inspection and Quarantine Bureau or HK public hospitals.