As China's urban development gradually shifts from scale expansion to the stage of optimizing and renewing the existing stock, the core goal of urban greening construction has changed from merely increasing the area of green space to enhancing the quality of space and the efficiency of public services. This transformation has made strengthening the public participation mechanism an urgent need for current urban greening work. Against this backdrop, the urban public green space construction model with the core concept of "People's Garden" has emerged. It emphasizes a green governance path oriented towards residents' demands and jointly built by multiple subjects, becoming an important exploration direction to solve the problem of the disconnection between traditional green space construction and public demands. However, at present, the practice of public participation in the construction of urban green Spaces in our country still faces many challenges - there are operational difficulties such as the lack of standardized guidelines for the participation process and the unsmooth feedback channels for residents' demands, as well as institutional shortcomings such as the ambiguous definition of the rights and responsibilities of the participating subjects in policies and regulations and the insufficiency of incentive mechanisms. The overall implementation path has not yet formed a clear framework. The relevant supporting institutional system is in urgent need of systematic improvement. As a typical example of public-participatory green space construction on a global scale, Setagaya Ward in Tokyo, Japan, has been focusing on the needs of urban refined management since the 1990s. Through a combination of policy guidance, mechanism innovation, and community mobilization, it has systematically promoted the institutionalization and systematization of the entire construction process. After more than three decades of practical exploration, A public-participatory green space construction model that is both operational and has demonstration value has been formed. This study conducts in-depth exploration around three core dimensions: First, it systematically sorts out the development trajectory of public participation in green space construction in Japan, from the rise of civic movements to the transformation of community building after the bubble economy, clarifying the changes in policy-driven and social demands at different stages; Secondly, taking Setanagaya District as the empirical research object, through literature analysis and field investigation, the organizational structure of its public participation in green space construction is analyzed in detail, and the policy framework including the detailed implementation rules of the "Urban Park Law", district-level special regulations, and the community building subsidy system is systematically sorted out. And summarize its supporting system in terms of fundraising, technical guidance, publicity and promotion, etc. Thirdly, for the key hub organization, Setagaya Trust & Community Design, core members were selected to conduct semi-structured in-depth interviews. A comprehensive assessment and reflection were carried out on its green space construction practices from dimensions such as practical effectiveness, existing challenges, and sustainability. Summarize successful experiences and room for improvement. Based on the above research, this paper ultimately returns to the reflection on the construction of "People's Gardens" in our country. In light of local realities, it puts forward targeted suggestions from three aspects: policy improvement, organizational optimization, and action innovation. At the policy level, it is necessary to accelerate special legislation to clarify the rights and responsibilities of participants. At the organizational level, a cross-departmental collaborative platform should be established to promote resource integration. At the action level, it is necessary to stimulate residents' continuous participation motivation through capacity building and cultural cultivation, thereby providing practical references for the construction of public-participatory green Spaces in the context of urban stock renewal in China.