Using the formal implementation of the 2012 Green Credit Guidelines (GCG) as an exogenous shock to construct a quasi-natural experiment, we study the impact of green credit policies on the inefficient investment of heavily polluting firms in China's listed companies from 2008 to 2020. We find that green credit policies can significantly alleviate the inefficient investment of heavily polluting enterprises. By reducing agency costs and long-term liabilities, green credit policies mitigate the problem of inefficient investment in heavily polluting firms. Moreover, the mitigating effect of green credit policies on the inefficient investment of heavily polluting enterprises has significant heterogeneity in terms of property rights, internal characteristics.