Hello! I'm Cambodian. How many day i can stay in China (Zhenshen) if i apply for tourist L ?

That depends on the figure between the DURATION OF EACH STAY and DAYS AFTER ENTRY. Usually, the duration of stay for tourist L type is 30 days. Sometimes, you may be given 60 days or 90 days.

Hello thank you so much for replying me. I have one more question. Let's say i went to China for one week and I come back to Cambodia. Do I require to make a new one to visit China again if it still within the 30 days from my last entry permit?

If your last visa has double or multiple entries, you can use it, and no need to apply for a new one for re-entering China. Otherwise, you need to make a new visa then.