When you work in a school in China your details are registered with the authorities. If you leave this school and want to move to another you must obtain a Release Letter from the school. With this, your new employer will be able to register you. Without it, you will not be able to be registered at the new school and – in the eyes of the authorities – will still be working in the first school.
The Release Letter is an incredibly important document and you must obtain one. By law the school must give it to you within 30 days from you leaving them, regardless of whether you left them on good or bad terms.
The letter needs to be completed and officially stamped by the school.
Cost
A Release Letter is free and you should not pay for one.
However, some schools demand payment for it. Some schools will even include in the contract a clause saying you will need to pay for it and then demand between 5,000 CNY up to 25,000 CNY or about $800 USD (€633, £509) to $4000 USD (€3165, £2545)!
But this is totally illegal.
You have every right to demand a Release Letter when you leave a school and you do not have to pay a single penny for it. However, if you find yourself in a position where your employer is demanding money for it or delaying giving it, then you should contact the China Foreign Teachers Union who will be able to advise you and help with obtaining your Release Letter from your old employer.