Beyond Additivity: Digital–Green Synergy in Sustainable Development Policy Systems and Corporate ESG Performance

Against the backdrop of deepening coordinated policy governance, the systemic synergy between digitalization and green transformation policies and their impact on corporate ESG performance has become a key issue requiring urgent exploration. Unlike existing studies that focus on the effects of individual policies, this paper adopts a policy system synergy framework to systematically investigate the impact of the coordinated implementation of big data administrative reform and low-carbon city pilot policies on corporate ESG performance. Using a sample of Chinese A-share listed companies from 2010 to 2022, this study applies a multi-period difference-in-differences (DID) method for empirical analysis. The findings show that the systemic synergy between digital and green policies significantly enhances corporate ESG performance, with this promoting effect substantially stronger than that of single pilot policies. Further causal re-identification using a double machine learning (DML) approach verifies the robustness of the baseline conclusion. Heterogeneity analysis indicates that the synergistic effect of digital and green policies is more pronounced in firms with higher levels of digital transformation, greater patient capital, and heavier tax burdens. Mechanism tests reveal that digital–green policy synergy improves ESG performance by enhancing external supervision from government, society, and the market, increasing green government subsidies, and incentivizing firms to engage in green innovation. At the same time, policy system synergy also reduces firms’ perceived uncertainty regarding economic policies and stabilizes their expectations, further enhancing ESG performance. This paper extends the research on the determinants of corporate ESG performance from the perspective of system synergy governance, providing new empirical evidence for understanding the interaction mechanisms between digital governance and green transformation policies.