Paper describes the relationship and mechanism of environmental regulations on carbon emission efficiency from the two dimensions of structural upgrading and efficiency improvement, and studies how environmental regulations improve urban carbon emission efficiency. Based on the data of 279 cities in China from 2006 to 2019, non-parametric percentile self-extraction method, stepwise regression method, Sobel test and interactive regulation model were used to verify the influence paths, and threshold model was used to explore the regulatory effects of environmental regulations under different paths. The results show that: Firstly, environmental regulations promote urban carbon emission efficiency, but there is regional heterogeneity; Secondly, environmental regulations improve carbon emission efficiency by promoting industrial structure upgrading, green technology innovation and energy efficiency upgrading, industrial structure rationalization and industrial agglomeration "mask" the incentive effect of environmental regulations; Thirdly, environmental regulations have various threshold effects and regulatory mechanisms for improving carbon emission efficiency. When giving play to the dual incentives of environmental regulation on carbon emission efficiency structure and efficiency, it is necessary to pay attention to the dimensions of different paths in order to improve the accuracy and grasp the intensity. Key words: Environmental regulation; Carbon emission efficiency;