As one of the fundamental institutional arrangements in the capital market, the delisting system has been progressively refined in recent years. Concurrently, auditors’ responsibilities as the “gatekeepers” of the capital market have been increasingly emphasized. Against this backdrop, this paper empirically examines whether sharing an auditor with firms subject to delisting risk warnings generates a spillover effect on the audit quality of other normal listed companies. Using a sample of A-share listed companies in Shanghai and Shenzhen from 2021 to 2024, the study finds that auditors serving firms facing delisting risk warnings significantly improve the audit quality of other normal listed companies audited by the same auditor in the same year. Mechanism testing indicates that the spillover effect is primarily driven by increased audit input, enhanced audit prudence, and strengthened identification of material risks. Heterogeneity analysis further reveals that this effect exists for both first-time and repeated delisting risk warnings and is more pronounced in large audit firms, among auditors with greater industry expertise, when the shared auditor is the lead signing auditor, and in firms with higher financial risk, stronger internal control quality, and lower institutional investor ownership. From the perspective of shared auditors, this paper confirms the regulatory spillover effect of the delisting risk warning system and provides policy implications for further refining the delisting system and strengthening the role of auditors as key market intermediaries.