I am going to China after I visit Cambodia

If you want to apply for a tourist L type from Cambodia, first, you need to provide a filled-out application form affixed with a passport-style photo, your passport and its photocopy, valid visa for Cambodia, round trip air tickets and hotel reservation. Next, submit the application to the Chinese embassy.

i am curious as to the sequence .. that means you must buy the air ticket and book the hotel .. before you apply for entry permit ? what if the visa is not approve ? the air ticket and the hotel cost will be lost ?

You can book the air ticket and hotel online, and then the airline or the hotel will send you the order form. You don't need to buy the air ticket and hotel reservation.