With the substantial increase of traffic flow in high-density cities, particulate matter pollution has been a serious problem in urban blocks. As an important composition of urban landscape, its plant morphological parameters have an important impact on air quality of street. Taking a block in Guangzhou as the research subject while using field monitoring data, the accuracy of ENVI-met software in dealing with block scale PM_2.5 simulation characteristics is verified. Then, the combination of various morphological parameters of plants on both sides of the street in the case area is modeled and numerically simulated. The result of ENVI-met shows that the model is suitable for simulating the traffic source PM_2.5 of high-density urban blocks. The simulation results of several groups of plant morphology show that the height of street trees is recommended to be about 10 m, which can effectively reduce the PM_2.5 of traffic source concentration. In combination with relevant specifications, it is recommended to set the trunk height as 3~5 m and the crown width as 5~7 m.