Abstract: Residual currents play a significent role in long-term transport and diffusion of pollutants in water bodies, and the field of residual currents can be altered by the shoreline changes caused by reclamation activities in the Bohai Bay. In order to investigate the changes of residual current field in the Bohai Bay before and after the reclamation, the hydrodynamic field and the Lagrangian particle moving trajectories in the Bohai Bay before and after the reclamation are simulated by using the hydrodynamic model and Lagrangian particle tracking model of software MIKE21, and the Eulerian residual current field and the detailed circulation structures in the Bohai Bay are obtained. By comparing the changes in hydrodynamic field, residual current field and Lagrangian particle trajectories before and after the reclamation, it can be concluded that after the reclamation the velocities of the maximum flood and ebb currents in most areas of the Bohai Bay are all decreased compared to those before the reclamation, and the directions of the maximum flood and ebb currents are changed in the waters near the reclamation area. The velocities of the residual currents are changed greatly in the waters near the shore and ports. The residual current field in the Bohai Bay exhibits four circulation structures, among which the clockwise circulation located near the Huanghua Port and the Binzhou Port and the counterclockwise circulation located at the southern bay mouth are significantly affected by the reclamation activities. The overall circulation structure in the Bohai Bay follows a pattern of inflow from the north and outflow from the south. After entering the bay from the northern part of the bay mouth, the currents flow inward and diverge into three branches in the southeastern sea area of Caofeidian, which flow southward, southeastward and southwestward, respectively. Of them, the southwestward branch further diverges near the Tianjin Port during the process of its flowing into the bay, and then these branches join the circulation structures on the north and south sides of the Tianjin Port.