This study investigates whether common auditors have an impact on firms’ green innovation. Using a sample of Chinese listed firms, we find the common auditor ties to firms with green patents are positively related to focal firms’ green innovation. When examining underlying mechanisms behind such effects, we observe that our main findings are more profound for focal firms with more opaque information, communicating with auditors intensively and audited by senior auditors, which indicates information sharing serves as the plausible mechanism. Cross-sectionally, our findings are more remarkable for non-SOEs, firms with lower financial constraints, firms located in regions with environmental courts, local auditors, auditors with green auditing abilities and firms in the same industry. Further analysis suggests that the common auditor ties to firms with green patents can further improve focal firms’ environmental performance and green patent citations, which in turn boosts market share of involved audit firms. Overall, we document that common auditors have a positive spillover regarding green innovation to connected clients through transferring valuable green expertise in a legitimate way.