The literature shows that a firm's environmental information disclosure is affected by internal and external factors. However, it is unclear whether internal control positively impacts a firm's green information disclosure. We collected data from the period 2010-2016 from either environmental reports or the environmental section of social responsibility reports of A-share listed companies in the heaviest polluting industries of the Chinese capital market, 1603 companies in total, and established an evaluation index for measuring firm greenness. Our research indicates that the level of internal control was positively correlated to the firm's greenness level, and deficiencies in internal control were negatively correlated to the firm's greenness level, indicating that high-quality internal control improves company green information disclosure. Pertaining to property rights, the internal control of state-owned enterprises had a significant effect on improving the level of environmental information disclosure. Among five elements of internal control, the internal environment, information and communication elements had a significant positive impact on firm greenness. Compared with samples with uncorrected major deficiencies in internal control, rectified companies' environmental information disclosure was greener. These findings provide empirical evidence for a comprehensive understanding of the non-financial reporting goals of firm internal control, and will become a useful reference for firm green governance decision-making.