Since the promulgation of "Several Provisions on Protecting and Improving the Environment (Trial Draft)" in 1973, the central and local governments have issued a large number of laws and regulations on environmental governance, which has become an important measure to promote environmental pollution control in China. Then, can the rule of environmental protection reduce the level of environmental pollution? This paper explores the impact of environmental rule by law on environmental pollution, and analyzes the mechanism of local environmental legislation on environmental pollution. On this basis, 108 cities in the Yangtze River Economic Belt are selected as samples and the municipal panel data from 2003 to 2017 are selected to empirically test the impact of environmental rule by dual difference method. The paper also verifies that industrial upgrading is the transmission mechanism of environmental legislation affecting environmental pollution, and verifies the research results of this paper by means of propensity score matching method, empirical test at sub-regional level and dynamic effect test, and puts forward relevant policy suggestions. The results show that:1) Local environmental legislation significantly inhibits environmental pollution, and the lag effect test results also show that local environmental legislation inhibits environmental pollution, which means that the emission reduction effect of local environmental legislation has a long-term mechanism; 2) The test results of the sub-regions along the middle and lower reaches of the Yangtze River Economic Belt also verify the conclusion that environmental legislation inhibits environmental pollution, which is consistent with the results of the full-sample test of the Yangtze River Economic Belt, indicating that the effect of local environmental legislation on inhibiting environmental pollution is relatively robust. The results obtained by the propensity score matching method also support the pollution control effect of local environmental legislation; 3) Further research on the transmission mechanism shows that environmental legislation inhibits environmental pollution through industrial upgrading, that is, industrial upgrading is the transmission mechanism of local environmental legislation affecting environmental pollution, which means that local environmental legislation stimulates enterprise innovation, promotes industrial upgrading, and inhibits environmental pollution. Therefore, the article finally puts forward the corresponding environmental policy recommendations such as from the overall to the proceeding of the rule of law to promote environmental governance, perfecting the system of local environmental legislation construction, expanding the transfer payment in field of environmental protection efforts, ensuring pollution control well-funded, increasing the environmental protection inspection standard, preventing "sports type" management mode. This paper analyzes the mechanism of environmental legislation on the environmental pollution from the perspective of the municipal level, empirically conducts a series of tests, and verifies the effect of environmental legislation on environmental pollution through the transmission mechanism, enriches the research on the environmental pollution control effect of the municipal level, and provides beneficial reference on environment pollution governance for local government.