In recent years, social media has had a crucial role in promoting governments to act more responsibly. However, few studies have investigated whether social media use actually leads to increased disclosure during environmental incidents, or how social media influences regional governments’ information disclosure, even though delayed and insufficient disclosure on relevant incidents is often widespread in China. In this article, we model information disclosure during environmental incidents as an evolutionary game process between the central government and local governments, and examine the role of social media on game participants’ strategy selections in the information disclosure game. The results indicate that social media plays an active role in promoting the regional government to proactively disclose information during environmental incidents through two mechanisms: the top–down intervention mechanism, and the bottom–up reputation mechanism. More specifically, social media can provide efficient information channels for the central government to supervise local officials’ limited disclosure during environmental incidents, essentially sharing the central government’s supervision costs, and thus improving its supervision and intervention efficiency. Social media helps focus the public’s attention on the limited disclosure of local officials in environmental incidents, and actively mobilizes citizens to protest to maintain their interests, placing considerable pressure on the reputation of local governments.