Pollution emission permits trading, as an efficient way, has been adopted by some developed countries. At present, the experimental pollution emission permits trading is in process in China. The authors analyze the economic essence of the trading with economic principles, and explains the advantage of the trading system , then comes to the point that there will be a same equilibrium point of trading whether the original permits is given away through auction or without cost. Finally it introduces a way to establish a system for original pollution emission permits trading and suggests that the original permits not be given to heavy polluting electric power plants.