The urban green space system is the only natural carbon sink in the city and plays an important role in the change of CO2 concentration. Through a case study of Shanghai Expo Park, the carbon sink capacity of different community types, structures and components were discussed, and the key factors affecting community carbon storage were analyzed. The results showed that there were 30 species of trees belonging to 27 genera and 17 families, 62 species of shrubs and vines belonging to 51 genera and 28 families, and 9 species of herb. The total carbon storage and average carbon density were 388.91 t, 80.53 t/hm2 (2017) and 399.82 t, 94.08 t/hm2 (2018). The tree species of Shanghai Expo Park were rich and the carbon storage increased. The carbon sink capacity of the community was increased in the mixed configuration of broad-leaved or coniferous-broad-leaved tree layer and shrub layer, broadleaf species, and coniferous species. Fine tree species for carbon sinking included Cinnamomum camphora (654.35±84.13kg), Pistacia chinensis (631.47±52.53kg), Ulmus parvifolia (538.47±40.35 kg), Bischofia polycarpa (435.50±62.25 kg), Zelkova schneideriana (386.76±36.83 kg). The community of the highest carbon density was C. camphora (No.25, No.48), and the larger annual increment of carbon density was C. camphora + U. parvifolia + Pterocarya stenoptera, C. camphora + Celtis sinensis + Sapium sebiferum, C. camphora + U. parvifolia. The contribution rates to community carbon density from high to low were tree age (31.44%), planting density (25.66%), tree species (11.95%), configuration structure (10.52%), species richness (10.50%) and site type (9.92%). Tree species, community density, and community structure should be considered during the plant community configuration. It can be improved the carbon sink efficiency and capacity in urban greening.