As a pivotal institutional tool for digital government construction and the market-oriented reform of production factors, the economic impact of public data openness on micro-level corporate behavior was systematically evaluated. Based on a sample of Chinese A-share listed companies from 2009 to 2023, the causal effect of public data openness on corporate performance and its underlying mechanisms were identified by employing a multi-period difference-in-differences (DID) model integrated with city-level pilot information. A significant positive effect of public data openness on corporate performance was revealed through benchmark regression. The reliability of this conclusion was confirmed by a series of robustness tests, including parallel trend tests, placebo tests, PSM-DID estimation, and the exclusion of contemporaneous policy interferences such as the "Broadband China" strategy and National Big Data Comprehensive Pilot Zones. Mechanism analysis indicates that corporate performance is enhanced through two primary transmission pathways: the alleviation of financing constraints and the promotion of corporate innovation. By serving as an authoritative signaling mechanism, public data openness reduces information asymmetry in credit markets and lowers credit acquisition costs. Simultaneously, it provides low-cost knowledge reserves that reduce R&D trial-and-error costs and stimulate patent output. Heterogeneity analysis further demonstrates that the performance-enhancing effects are more pronounced among enterprises in eastern regions, small-scale enterprises, non-state-owned enterprises, and non-high-tech firms. These findings provide empirical evidence and policy orientation for optimizing public data supply quality, mitigating the digital divide, and fostering the efficient utilization of data elements.