Abstract: [Purpose / Significance] The article takes the public cultural service provided by public libraries with the PPP mode in China as the research object, and proposes the concept of "library + documentary cinema line". This project can not only diversify public cultural services provided by public libraries, but also promote the healthy development of the documentary film industry. [Method / Process] The study briefly summarizes the status quo of the cooperation between public libraries and social capital, points out some problems in the development process, and analyzes the significance and feasibility of the "Library + Documentary Cinema" project. [Results / Conclusions] Some countermeasures are put forward, such as making efforts to open up the market and improve the effectiveness of publicity, establishing a correct concept, reasonable and legal charge, selecting appropriate partners, giving full play to the advantages of public libraries and providing special services, uniting multiple forces, and overcoming potential obstacles.

Key words: PPP mode, public library, social capital, public cultural service, documentary cinema