While many extant studies focus on the relation between financial performance and corporate social responsibility (CSR) reporting, less attention has been given to the shifting role of financial performance in CSR reporting in a changing institutional environment. The objective of this study is to investigate whether, why, and how institutional transitions affect the role of financial performance in CSR reporting. Using samples of A-share listed companies from 2008 to 2015, we separately examine the impacts of institutional transitions on firms' propensity to issue standalone CSR reports, the quality of voluntary CSR reports, and the quality of mandatory CSR reports. We find that financial performance buffers against external pressures brought by institutional transitions rather than only serving as a slack resource. By highlighting the buffer role of financial performance, our study provides deeper insights on the relation between financial performance and CSR reporting and contributes to extant institutional research on CSR reporting.