How can I apply for a China tourist visa if I am now studying in Thailand?

You can apply for a China tourist visa through Chinese embassy in Thailand. The processing time needed is 4 working days. The documents you need to prepare are as follows:
1.A valid passport as well as a copy of its information page: Your valid passport must have at least six (6) months of remaining validity and at least one blank visa page in it.
2.Application form: Both V2011A and V2011B.
3.Photo: one recent photo of 2x2 square inch.
4. A copy of the round-trip plane ticket and hotel booking in China.
5. Previously used China visa if any.
Generally, you will be given a single entry tourist visa, but it can be extended twice in China. Anyway, you can request a double or multi visa in your application form, and better provide detailed travel itinerary for those entries.