To legally work in China as a teacher you must enter the country with a 30 day Work (Z) Visa. Before the visa expires your school will need to apply for (sponsor) your 1 year residence permit.
To gain a Z visa need to get a copy of the Z class visa application and medical check form from your nearest Chinese Embassy.
After completing the Visa application form and your doctor completing the medical check form, send a copy to your school.
The school will use these forms to gain a letter of invitiation. When you receive the letter of invitation, take the letter, your application forms and passport photos to the nearest Chinese Embassy to apply for your Z visa.
The Z visa allows you to enter China and it will allow you to obtain a Resident Permit. The Resident Permit allows you to legally teach English in China. Your employer should help you apply for the Resident Permit after you have arrived in China on a Z visa. The Resident Permit is usually valid for 12 months and as with any other permit, you must have it renewed or leave China before it expires.