The biodiversity of plant species is of great significance for the maintenance and promotion of biodiversity in urban green spaces. It is an essential component of building a healthy and stable urban ecosystem. The scientific management evaluation of plant species biodiversity in urban green spaces is the foundation for implementing scientific planning and control, enhancing conservation technology, and promoting sustainable urban development. Developing scientific investigation methods is the foundation. In this study, taking the park green space, green buffer, and attached green space in the central urban area of Shanghai center as examples, according to the green space scale, green space shape, spatial layout, vegetation type, and ecological service function, the regional grid method, Sampling methods, point count method, and other sample plot setting methods were developed. 28 micro sample plots were selected for the Shanghai Expo Cultural Park, 272 primary road green space samples and 34 commercial service ancillary green spaces were surveyed using methods such as comprehensive survey, critical investigation, and special investigation to investigate new and excellent plants, backbone tree species, tone tree species, invasive species, ancient and famous trees, and three-dimensional greening plant species in the green space. A representative and highly operable plant species investigation method has been developed, providing the scientific basis for the precise pricing of urban green space biodiversity level, the development and utilization of new and excellent plants in newly constructed green spaces, and the improvement of plant species diversity protection in existing green spaces.