Green development pattern is an important starting point for building a new development pattern, and it is also the only way to achieve high-quality economic development. This paper takes the ecological industrial park as an example, uses the pollution discharge data at the firm level, and constructs a difference-in-differences model to test the impact of green development on the pollution discharge. Empirical studies have shown that the establishment of eco-industrial parks will significantly reduce the COD emissions in industrial wastewater. Further research found that the emission reduction effect of eco-industrial parks is more significant in the eastern developed areas and samples of non-state-owned firms. The mechanism analysis conclusion shows that eco-industrial parks achieve emission reduction effects by encouraging firms to increase purchases of pollution control facilities. This paper shows that in the next step of development, ordinary prefecture-level cities and central and western cities should be encouraged to actively declare eco-industrial parks. At the same time, they should also focus on improving the efficiency of corporate pollution control.