At present, urban green space construction should weight evenly between ecological-landscape effects and the establishment-management costs, and should take into consideration of saving requirement. It was necessary to establish the assessment system for plant communitys construction and improvement. A 4-leveled index assessment system was set based on indices which were selected according to Delphi expert consultation method, with all the weight calculated by Analytic Hierarchy Process (AHP) method. Then, the assessment system was applied to evaluate the green space plant communities in central Shanghai. The result showed that: due to low near-nature degree and a costly management, 51.4% of all the plant communities failed to meet the standard that ecological benefit should be in coordination with landscape benefit. To solve problems, new construction methods were introduced. In the construction of urban green space plant community, native species should be used to build the near natural plant community. The adoption of native species reflected the regional characteristics as well as the land-mark of the given region or city. Whats more, in order to reduce the management cost, the near natural management method was also recommended.