Old community renovation is now gradually receiving attention in China's urban construction development, and how to make its public space sustainable has become a research topic. This paper conducts a study of the current situation of public space in old communities from the surface to the deep through field research methods. This paper has summarized four spatial characteristics of public space in old communities, including the increase of boundary space; spatial function is polarized between context-specific user groups and complex but sustainable symbiotic systems. Based on these findings, this paper proposes three sustainable renovation considerations and strategies, which include respecting the rationales of the original space, stimulating the cooperation of stakeholders, and recreating the daily life of residents.