<p>Nuclear data bears a critical nexus with marine radioactive pollution surveillance, serving as the evidentiary foundation for source attribution and impact assessment. This article adopts an empirical research approach, integrating nuclide simulation modeling with radioactive monitoring data, to demonstrate that Japan’s discharge of Fukushima radioactive wastewater has resulted in the dispersion of radionuclides from inland waters into the North and West Pacific Transition Zones via ocean currents, thereby posing potentially irreversible, multigenerational threats to marine ecosystems. The current deficiencies in the international legal governance framework for marine pollution—combined with weak legal enforcement, a low level of cooperative consensus, and a transparency deficit in radioactive pollution monitoring—further exacerbate these risks. Accordingly, employing a doctrinal research method, this article examines the legal foundations for a Pacific Rim regional nuclear data regulatory framework and proposes a regional legal cooperation mechanism composed of legal principles, legal rules, organizational structures, and operational procedures. By constructing such a mechanism, the transparency of radioactive waste disposal monitoring data can be enhanced, the legal accountability challenges arising from Japan’s wastewater discharge mitigated, and regional consensus strengthened on nuclear data classification, monitoring, and disclosure—ultimately improving the safety of nuclear energy development and utilization within the Pacific Rim.</p>