Previous studies have found many factors that affect audit fees, such as company size, business complexity, internal control quality, firm characteristics and so on. Under the background of increasingly severe environmental problems, environmental risks will inevitably affect the business conditions of the company and thus affect the auditor’s judgment of risks. However, we know little about whether and how environmental risks affect audit fees. In this paper, we use the monitoring after the PM2.5 explosion as an exogenous event, and the propensity matching score method and the difference-in-difference model are used to study the relationship between environmental risk and audit fees. The empirical results show that, first, after the monitoring of PM2.5 began in 2012, those listed companies located in cities that take the lead in monitoring PM2.5 would be charged higher audit fees. Second, this relationship exists only in heavily polluting enterprises with low internal control quality.