Ecological environment governance is one of the core goals of high-quality development. In order to control pollution, the Chinese government has formulated many environmental policies, and incorporated the construction of ecological civilization into the overall layout of national development, which shows that the Chinese government attaches great importance to environmental governance, and also shows the severity of China's environmental governance. The environment is a typical public good, with a strong negative externality, the consumption of the environment is non-competitive and non-exclusive. As a rational "economic person", the government has the preference to pursue the maximization of its own interests. The characteristics make the government's rights and responsibilities are not clear in the process of governance of the environment, the lack of environmental governance power and other issues are not uncommon, to a certain extent, aggravating the difficulty of environmental governance. As an important means of environmental governance, can environmental decentralization and environmental protection legislation stimulate the motivation of local government environmental governance and reduce the level of environmental pollution from the perspective of incentive mechanism and accountability mechanism? This paper explores the impact of environmental decentralization and environmental protection legislation on environmental governance, and analyzes the dynamic mechanism of environmental decentralization and environmental protection legislation on environmental governance, on this basis, taking 27 central cities in the Yangtze River Delta as a sample, selecting municipal panel data from 2003 to 2019, using the dual difference method to empirically test the impact of environmental decentralization and environmental protection legislation on environmental governance, and verifying the research results of this paper through the tendency score matching method, dynamic effect test, placebo test, etc., and puts forward relevant policy suggestions. Environmental decentralization encourages the government to carry out environmental governance, effectively reduces the level of environmental pollution in the Yangtze River Delta, and environmental decentralization has obvious lagging effect on environmental pollution in the third phase of environmental pollution, and its impact is long-term. Compared with environmental decentralization, environmental protection legislation has a weaker effect on environmental pollution in the Yangtze River Delta urban agglomeration, and is tested through dynamic effect testing, increased control variables and placebo testing, etc., to make the results more reliable; It is worth noting that the environmental pollution control momentum of the combination of environmental decentralization and environmental protection legislation and policies is more significant, and the inhibition effect of the two policy combinations on environmental pollution is higher than the policy impact of the two separately. Therefore, the article puts forward corresponding environmental governance policy suggestions from the aspects of establishing regional environmental coordination and governance linkage, strengthening the construction of the rule of law, and encouraging environmental governance of various entities, continuing to give play to the role of environmental decentralization in long-term commitment to pollution, improving the regional environmental protection legislation standard system, strengthening the interactive effect of cooperative governance between environmental decentralization and environmental protection legislation, and enhancing the driving force of environmental governance. This paper analyzes the dynamic mechanism of environmental decentralization and environmental protection legislation on environmental governance from the perspective of the municipal level, and conducts a series of empirical tests to enrich the research on environmental governance at the municipal level, and verifies the impact of environmental decentralization and environmental protection legislation on environmental governance through multi-angle robustness test, providing useful reference for local governments to govern the environment.