Can I go back to China through customs after taking drugs in Cambodia?

Of course. Having a history of drug abuse is not a condition for prohibiting returning to China. You can sign up for returning to China if you have a history of drug abuse. However, if you take drugs before boarding the plane and returning to China, even if you don't carry them, getting off the plane is equivalent to taking drugs at home. According to different situations, the Public Security Administration Punishment Law and the Drug Rehabilitation Regulations shall apply.