Abstract: The Yangtze River Economic Belt is a pivotal region for high-quality economic and social development and a strategic area for ecological civilization construction in China, so the policy implementation efficiency within the territory has a significant meaning to the sustainable development of the whole region. To address the insufficient research on the policy diffusion mechanisms in this area, we investigate the Yangtze River Protection Law through a policy diffusion lens, developing an integrated analytical framework that couples the Bass diffusion model with rough set theory to unravel spatiotemporal diffusion patterns and driving factors. Key findings include: ① The policy diffusion exhibits a gradual sigmoidal curve, proceeding through three distinct phases, preliminary argumentation period (2019~2020), rapid implementation period (2020~2022), and deepening period (from 2022 to the present), with internal imitation effects predominantly driving the adoption dynamics; ② Spatially, a hierarchical diffusion pattern emerges, characterized by early adoption in core cities followed by adjacent regions; ③ Rough set analysis identifies industrial structure and technological capacity as the most critical drivers. By innovatively merging policy diffusion theory with rough set methods, we elucidate the multidimensional transmission mechanisms of basin-scale legal policies and propose a dual-engine strategy that prioritizes industrial and technological synergies. These insights establish an empirical foundation for a coordinated governance framework integrating legal constraints, industrial upgrading, and technological innovation in the Yangtze River Economic Belt, facilitating the transformation of ecological civilization construction from institutional design to practical effectiveness.