The carbon sequestration capacity of urban trees plays an important role in offseting urban greenhouse gas emissions and regulating urban carbon balance. However, greenhouse gas will also be generated in the process of planting and maintenance of urban trees. From the perspective of carbon budget, the net carbon sequestration capacity of urban trees can be evaluated more comprehensively and scientifically. Based on life cycle assessment, the biomass equation method and emission factor method were used to calculate the life cycle carbon sequestration and carbon emission of 32 urban woody tree species in Beijing. The results showed that the average life cycle carbon sequestration and carbon emission of the tested tree species were 222.441 kg/plant and 90.545 kg/plant, respectively, under the Beijing primary conservation management standard. The carbon sequestration and carbon emission in the whole life cycle of different life types of urban tree species were obviously graded, and the overall performance was deciduous arbor > evergreen arbor > small arbor > shrub. Twenty-one species such as Platanus acerifolia, Fraxinus pennsylvanica, Populus tomentosa and Koelreuteria paniculata had positive effects on the carbon sink capacity of urban green space, while eleven species such as Buxus sinica var. parvifolia, Euonymus japonicus, Prunus serrulata var. lannesiana were the opposite. The reason is not only related to their biological characteristics, but also related to their application form in pursuit of specific ornamental effects. Based on the research results, low-carbon plant landscape construction strategies are proposed from the aspects of carbon sink increase and carbon emission reduction.