Living in Cambodia but I am Spanishm, so what about the visa issue to China?

Generally speaking, you may need to provide your valid passport, application form with recent taken photo, your round trip tickets to China, your hotel bookings in China, bank statement and working proof if any. Besides you need to provide other documents the embassy requires.
Personally speaking, you are suggested to embassy first to get a detail documents list, so that you can avoid troubles.

Thanks a lot1