It is very important to protect the urban biodiversity. Urban parks are the main body of urban greenbelt system, which also are the place that biodiversity highest centralized in city. It can provide the basic data for urban biodiversity conservation by the research on the plant diversity of park greenbelt in urban. In this study, a systematic investigation on the plants of some parks of Beijing city was made, that the species composing of plants in urban park greenbelt are analyzed, and the characteristic of plant biodiversity was calculated and discussed, intending to provide scientific gist for the ecological urban construction in Beijing city. The results showed that there were 393 plants species, which belonged to 251 genera and 90 families in Beijing parks. Among them, 281 species were Beijing native plants, which were accounted for 71.50% of total plants species; 62 species were introduced from other regions of China, 15.78% of total parks plants ; and 50 species were introduced from foreign countries, 12.72% of total plants. The herbage had the highest species richness in park greenbelts, shrub species secondly, the arbor was a little lower than shrub. In the mass, the park plants had a high species diversity level.