In order to solve the problem of low coverage rate when nodes are deployed randomly in underwater three-dimensional (3D) sensor networks, an underwater 3D sensor network coverage algorithm based on vertical sampling is designed to improve the coverage and connectivity of underwater 3D sensor network. The coverage algorithm of underwater 3D sensor network based on vertical sampling firstly samples the 3D monitoring area in vertical plane, and then samples the plane in a straight line, which transforms the coverage problem of 3D space into the optimal problem of linear coverage. From the local to the whole, the goal of optimizing the coverage of the whole 3D network is achieved. The simulation results show that in the 100 m×100 m×100 m 3D monitoring area, the vertical sampling algorithm can increase the coverage by about 4%~28% compared with the 3D random deployment strategy, and the maximum degree of increase is obtained when the number of nodes is 40.