Strategic emerging industries serve as a new driving force for the high-quality development of China's economy, and their Environmental, Social, and Governance (ESG) performance is a crucial standard for assessing their ability to achieve sustainable development. This paper examines the impact of financial flexibility on the ESG performance of Chinese companies, using data from A-share listed companies in China from 2014 to 2023. The study also explores the transmission mechanisms and heterogeneity of this effect across external environments and internal governance. The findings indicate that financial flexibility significantly enhances ESG performance in Chinese listed companies. This conclusion holds after several robustness tests, including Two-Stage Least Squares (2SLS), Propensity Score Matching (PSM), and System Generalised Method of Moments (GMM). Furthermore, the enhancement effect is stronger in firms with higher investor attention, those in heavily polluting industries, companies with better governance, and those facing higher environmental uncertainty. Mechanism analysis reveals that financial flexibility affects ESG performance through green technological innovation and accounting information transparency. The study contributes to the literature on the economic consequences of financial flexibility and extends the understanding of the mechanisms and contexts in which corporate ESG performance can be improved.