Based on the data disclosed by listed companies in Shanghai and Shenzhen from 2012 to 2018, this paper discusses the specific effect of enterprise internal control on the scale of environmental protection in_x0002_vestment, and tests the regulatory effect of different provincial marketization degrees on enterprise internal control and environmental protection investment. The results show that: the effectiveness of internal control is positively correlated with enterprise environmental protection investment; the degree of provincial marketization will significantly promote the positive correlation between the effectiveness of internal control and enterprise environmental protection investment. At the same time, it is found that for the state-owned listed enterprises, the degree of marketization in their provinces will significantly enhance the positive correlation between the effectiveness of internal control and the scale of enterprise environmental protection investment. This paper verifies the role of internal control in promoting enterprise environmental protection investment, enriches the research on influencing factors of enterprise environmental protection investment, and provides beneficial exploration for further improving enterprise environmental governance ability.