As society continues to develop, a growing body of research is focusing on how informal institutions, such as culture, influence corporate behavior and economic outcomes. The aim of this study is to explore the impact of cultural inclusiveness, as a non-formal institution, on firm performance. Using Chinese A-share listed firms as our sample, we employ econometric methods to analyze the relationship between cultural inclusiveness and firm performance. Our findings reveal that cultural inclusiveness enhances firm performance, particularly evident in regions with higher levels of cultural inclusiveness, where firms tend to exhibit higher return on equity. To address concerns of endogeneity, instrumental variable regression using regional topographical changes is employed. Mechanism testing indicates that cultural inclusiveness primarily improves firm performance by reducing financial constraints and optimizing employee structure. Additionally, the study finds that cultural inclusiveness has a more pronounced impact on firms with higher corporate social responsibility (CSR) performance as well as those with greater investment in research and development (R&D). This study provides a comprehensive empirical explanation of how cultural inclusiveness influences the sustainable operation of businesses.