Abstract: Through the finite element analysis of the north anchorage caisson of the Fourth Nanjing Yangtze River Bridge, the section to control the safety of the caisson during dewatering sinking is determined, and the monitoring instruments are installed. The stress, strain, bearing reaction force and lateral earth pressure during dewatering sinking are acquired. The results show that the worst condition for the structural safety occurs at the beginning of dewatering sinking of the caisson with a large span caused by excavation. The bearing reaction forces of cutting edge and cross walls change with the variation of support conditions. The convex and concave of the caisson wall can reduce the side friction effectively.