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Green space interacts with particulate matters (PM) from urban atmosphere and road dust is a main source of urban PM pollution. We designed a dusting experiment of 21 days to examine the variations of pigments, gas exchange, height increments, and biomass of Sophora japonica seedlings (the most popular tree in Beijing) under 0, 1.45, 3.78, 9.02 and 16.64 g/m2 urban road dust loads. Along with the rising dust loads, total chlorophyll and net photosynthetic rate had logarithmic droppings, from 1.37 ± 0.10 to 0.42 ± 0.03 mg/g and from 9.87 ± 0.18 to 5.69 ±0.69 µmol/m2/s, respectively. The root-shoot ratio of biomass logarithmically increased between 2.17 ± 0.51 and 2.73 ± 0.21. The height increments had a linear decline between 3.8 ± 1.0 and 1.5 ± 0.2 cm. Gas exchange parameters decreased fast in the initial dusting time and then reduced slowly or even increased. When dusted with the maximum foliar dust load of Beijing's street trees for 21 days, photosynthetic performance of S. japonica would decrease by 16%; height increment of S. japonica would decrease by 17%. Leaf biomass decline caused by dust might be a potential risk for street trees. Using plants like S. japonica as street trees or other green spaces could be a good measure to mitigate PM pollution.