Based on the perspective of sustainable development, using the implementation of the Shanghai-Shenzhen-Hong Kong Stock Connect trading system as a quasi-natural experiment, this study selected data from A-share listed companies in Shanghai and Shenzhen stock market from 2010 to 2020 to examine the impact mechanism of capital market opening on high-quality development of enterprises. The research finds that the implementation of the Shanghai-Shenzhen-Hong Kong Stock Connect trading system has improved the total factor productivity and ESG level of enterprises, and promoted the high-quality development of enterprises. This conclusion is still valid after a series of robustness tests; The trading system of the Shanghai-Shenzhen-Hong Kong Stock Connect can promote high-quality development of enterprises through technological innovation effects, internal control effects, and external supervision effects; Based on the heterogeneity test of regional institutional environment, industry attributes, and property rights, it was found that the opening of the capital market has a greater promoting effect on the high-quality development of regions with lower institutional environment, heavily polluted industries, and state-owned enterprises. This article provides new evidence for further expanding high-level financial openness to the outside world and achieving high-quality economic development.