河长制是我国地方政府为破解当前流域环境治理困局而进行的政策创新，这种水环境责任承包制简单易行且有效实用，很快在全国形成扩散效应。从无锡市2007年探索实施的一项过渡性应急治理之策，最终演化成为我国常态化的生态环境保护制度，其创新扩散模式在实践中被烙上了鲜明的中国特色。因此，本研究也有助于为我国其他相似政策场域的创新扩散现象提供一些本土化的解释。 基于政策创新扩散的理论视角，本文对河长制在我国政治与政策环境中的时空演进过程进行分析，发现在时间维度，整个创新扩散过程可以分为“省内扩散”和“省际扩散”两个阶段，其中，河长制在各省份间的创新扩散曲线呈近似的S型，经过准备期、显现期、加速期，当前扩散积累量已接近饱和，扩散速率趋于稳定，政策体系也日臻成熟和完善；在空间维度，以江苏、浙江为代表的华东地区作为河长制的政策开拓者与先行者，率先进行政策创新和政策试验，并引起其他地区的模仿和借鉴，形成先行-跟进的扩散机制。 借鉴贝瑞夫妇提出的美国州政府创新扩散总模型，结合河长制时空演进机理，本文归纳了影响河长制创新扩散的三类潜在因素，形成一个包含外部府际扩散因素、内部禀赋决定因素、舆论因素的整合模型，并运用事件史分析法对2010-2017年我国31个省级政府政策创新扩散行为进行研究，结果表明：外部因素中，区域效应带来的竞争压力对河长制创新采纳起到显著的正向推动作用，可见同一地区政策决策者间隐性的政绩竞争和“政治晋升锦标赛”普遍存在；内部因素中，经济水平、政策内生需求、水环境治理能力与政策采纳概率的相关性假设均得到证实，因此各省自身的资源禀赋是助推河长制创新扩散的关键因素；舆论因素中，中央主流媒体的报道则显著提升了省级政府采纳河长制的概率和优势。 鉴于河长制在我国省级政府间的创新扩散路径呈现出区域竞争效应突出，内部资源禀赋保障，中央主流媒体助推的主要特征和基本格局，本文提出三条政策创新扩散路径的优化建议，即发挥政策试点标杆作用，化竞争压力为学习动力；提升地方政府资源禀赋，强化自主政策创新意识；增强主流媒体推动作用，完善政策扩散动员机制。综合把握河长制创新扩散规律，形成良性、协同、高效的政策扩散路径，既是政府以“河长制”实现“河长治”的因应之道，也是推动流域生态环境治理体系与治理能力现代化的必由之路。

The River-Chief System is a policy innovation by the local government to respond the current watershed environment governance dilemma. The system of contracted responsibility for water environment has been diffused around the whole country soon because it is simple, effective and practical effect. A transitional emergency management policy explored and implemented in Wuxi City in 2007 finally evolved into a normalized ecological environmental protection system in China, and the innovation diffusion model has been branded with distinctive Chinese characteristics in practice. Therefore, this study also helps to provide a localized interpretation of the phenomenon of innovation diffusion in other similar policy field in China. Based on the perspective of policy innovation diffusion theory, this paper analyzes the temporal and spatial evolution process of the River-Chief System in Chinese political and policy environment, and finds that the whole innovation diffusion process can be divided into “diffusion within Jiangsu Province” and “diffusion among provinces” in the temporal dimension. And in the second stage, the innovation diffusion curve of the River-Chief System is similar to the S-shape. After the preparation period, the development period and the acceleration period, the current diffusion accumulation is close to saturation, the diffusion speed tends to be stable, and the policy system has gradually matured and improved as well. In the spatial dimension, as the policy pioneers of the River-Chief System, the East China Region represented by Jiangsu and Zhejiang Province took the lead in policy innovation and experiment. It has caused the policy imitation and reference in other regions, and forms a leader-laggard diffusion mechanism. According to the temporal and spatial evolution mechanism of the River-Chief System, this paper summarizes three kinds of potential factors that influence the diffusion of River-Chief System based on the general model of American state government innovation diffusion proposed by Berry FS and Berry WD, forming an integration model including external intergovernmental relations factors, internal resource and endowment factors, and public media factors. Using the event history analysis method to study the policy innovation diffusion behavior of 31 provincial governments in China from 2010 to 2017, the results show that the regional competition pressure has played a significant positive role in promoting the diffusion of policy innovation among the external factors. It can be inferred that the implicit political achievements competition and official promotion tournament among policy decision-makers in the same region are widespread. Referring to the internal factors, the positive correlation between economic level, policy endogenous demand, water environment governance capacity and the policy adoption probability has been confirmed, indicating that a province's own resource endowment is the key factor to promote the innovation diffusion of the River-Chief System. As for the public media factors, the reports of the central mainstream media have significantly increased the probability and advantages of the provincial government adopting the River-Chief System. The innovation diffusion path of River-Chief System among provinces in China shows the main characteristics and basic pattern of outstanding effect from regional competition and central mainstream media, with the internal resource endowment as a guarantee. Therefore, this paper proposes three optimization suggestions for the diffusion path of policy innovation, including transforming competitive pressure into learning motivation under the demonstration role of the policy pioneers, enhancing the level of resource endowment and the awareness of policy independent innovation of local government，and improving the policy diffusion mobilization mechanism with the strengthening of the mainstream media promotion. As a result, it is necessary to implement the River-Chief System and establish an optimized, efficient and coordinated path for policy proliferation under the law of policy innovation diffusion, which is not only the way to ensure the river long-term governance but also the only way to modernize the government's watershed ecological environment governance system and governance capacity.