This study was about undertaken to assess the impact of Hg and As on the surface environment system in Shanghai urban district. Particle size effect of Hg and As in surface dust was researched, and the result showed that the high values centralized in the range of ＜125 μm and particle size effect played a role in pollutant concentrations. The contents of contaminants decreased with the increasing of flow time except for Hg of highway. The consequence of environmental behavior of Hg and As in multi-media environment of surface dust and rainfall-runoff system proved that surface dust made a great contribution on the load in rain-fall runoff. The EMCs of Hg in roofing and highway were similar, but EMCs of As were opposite to them. The result indicated that the magnitude of the first flush phenomenon which was affected by characterization of rainfall and different land use types was found to be greater which was closely linked with precipitation.