<p>The coexistence of stringent environmental targets and intense tax competition among Chinese provinces creates a critical tension that directly affects pollution outcomes. This study employs the ARDL-ECM model and a dynamic heterogeneous panel estimation approach using provincial-level data to examine both the short- and long-run impacts of environmental regulation and tax competition on pollution emissions. The results reveal both short-run adjustments and a long-run equilibrium among environmental regulation, tax competition, and pollution emissions. Environmental regulation shows a policy-oriented effect, effectively reducing air and water pollution in both the short and long run, regardless of regional, economic, fiscal, or environmental heterogeneities. By contrast, tax competition exhibits an economy-oriented effect, intensifying air pollution across both time horizons, especially in central and western regions and in provinces under greater economic and fiscal pressures. Furthermore, tax competition undermines the long-term effectiveness of environmental regulation, weakening the efficiency of local environmental governance. Finally, while government-led regulation has achieved sustained improvements in pollution control, enterprise-level management remains ineffective. These findings suggest the need to strengthen institutional mechanisms that limit harmful tax competition, enhance corporate environmental responsibility, and improve the long-term effectiveness of local environmental governance in China.</p>