Abstract: This paper comprehensively uses the difference-in-difference (DID) and the system generalized method of moments (SYS-GMM) estimation method to test and identify the implementation effect, emission reduction mechanism and emission reduction effect of environmental regulation in Western China. The conclusions are as follows: (1) The implementation of the new environmental protection law has effectively reduced the emission intensity of pollutants in the western region, and the emission reduction effect is significant. (2) The emission reduction effect of the new environmental protection Law mainly plays a role through four mechanism variables including the level of urbanization, the level of economic structure, the intensity of scientific and technological investment，the circular production capacity.(3) The level of urbanization, the intensity of scientific and technological investment， the circular production capacity have greater emission reduction effects, while the level of economic structure has less emission reduction effects. (4) The pollution emission intensity in the western region has obvious cumulative lag effect.