The PPP model brings a new development path to the rural mutual-aid system for the elderly. From the perspective of the new institutionalism theory, this paper compares the institutional environment of the PPP model between China and Germany from three aspects of mandatory, normative and cognitive features, and explores the construction strategy of the PPP system for the elderly based on mutual-aid in rural China. As far as Germany is concerned, the federal government has implemented appropriate policies, laws and regulations in the construction of “multi-generation house”, and its social capital and people also actively participate in the construction of “multi-generation house”, thus forming an advanced mutual-aid system for the elderly. The construction of the rural mutual-aid PPP system for the elderly is still in the initial stage in China, and relevant policies, laws, and regulations are not yet perfected. The enthusiasm of social capital and the awareness of mutualaid of rural residents also need to be improved. Based on the comparative analysis between China and Germany, this paper puts forward some suggestions, such as optimizing policy and legal environment, broadening financing channels, innovating public-private risk sharing mechanism, and popularizing digital old-age life, so as to promote the development of China’s rural PPP system for the elderly with mutual assistance.