Abstract: The Hangzhou Bay is directly adjacent to the Yangtze River Estuary and changeable hydrological characteristics. As and Hg are two kinds of heavy metals, which are highly toxic to environment and organisms in the ocean. Therefore, it is highly essential to study the distribution of As and Hg in seawater off the Hangzhou Bay, which will be immensely crucial for the enhancement of the marine ecosystem. The concentration of As and Hg in seawater off the Hangzhou Bay were investigated in the summer (August) and autumn (November) of 2020. We analyzed the pollution degree and distribution characteristics, and the influencing factors were discussed. The results showed that the concentrations of As in summer and autumn were in the range of (0.134～1.728) and (0.318～1.142) μg/L, respectively. Correspondingly, the concentrations of Hg were in the range of (0.021～0.109) and (0.004～0.040) μg/L, respectively. In general, the horizontal distribution of As and Hg concentrations were higher in the nearshore sea area, which also indicated the influence of terrestrial input. The concentration of As was slightly higher in autumn as compared to in summer, while Hg was significantly higher in summer than in autumn. There were also concentration differences between the surface and bottom. In addition to terrestrial input, the distribution of As and Hg was also affected by the Changjiang Diluted Water, current, sediments, suspended solids release, biological activities, atmospheric sedimentation as well as temperature, dissolved oxygen (DO), pH in seawater.