Understanding China’s environmental policy agenda is an important issue for advancing socialist ecological civilization in the process of promoting Chinese modernization. Based on the “second-order coupling” analysis framework constructed after the modification of the multi-source flow theory, this paper reviews the process of upgrading the river chief system, an environmental policy with distinctive Chinese characteristics, from local exploration to national action, which is helpful to reveal the operating logic of China’s environmental policy agenda. In the initial phase, although policy innovations represented by the river chief system in Wuxi temporarily alleviated local water environmental governance issues, at the national level, the problem stream, policy stream, and political stream of the river chief system only achieved multiple partial coupling. Consequently, it remained in the stage of local diffusion and exploration. Nonetheless, the first-order local coupling of the river chief system has also won the attention of central government departments and driven the national agenda. At the second phase, the problem of water governance in different contexts across the country is still prominent and the dominant political flow has undergone significant changes. Continued local explorations and interactions between central and local authorities facilitated a fundamental reconstruction of the policy stream. Coupled with proactive actions from central policy advocates, this led to the complete coupling of the three streams, enabling the river chief system to finalize a national policy and commence nationwide promotion.The results show that due to the high complexity and multiple contextuality of China’s national governance, the ‘second-order coupling’ shown in the case of the river chief system reflects the theoretical value of ‘loose coupling’, which provides a new theoretical perspective for understanding the resilience and adaptability in China’s policy process, and also provides useful theoretical references for improving China’s environmental governance system and promoting the construction of ecological civilization.