Do international students need a guarantor to rent a house in Britain? How to rent a house without a guarantor?

Not necessarily. No guarantor was required before renting a house. Generally speaking, you only need to provide a letter of confirmation from the school.

Your situation is special, because you are still in China. I suggest you apply to the school to help you arrange temporary accommodation, and then consider renting a house when you arrive in Britain. And the school also has teachers who are responsible for managing students' accommodation. They have a lot of information about housing. Just tell them your requirements.