A numerical approach based on the solution of the Reynolds-averaged Navier-Stokes (RANS) equations using the shear-stress transport (SST) turbulence model has been employed to investigate the hydrodynamic performance and flow of tunnel thrusters. The flow passages between adjacent blades are discretized with prismatic cells so that the boundary layer flow is resolved down to the viscous sub-layer. The hydrodynamic performances predicted by the quasi-steady approach agree well with the experimental data for three impellers covering a range of blade area and pitch. Through analysis of the flow field, the reason why the hub of impeller also contributes to thrust which can amount to 40%—60% of the impeller thrust, and the mechanism of the impeller inducing an axial force on the hull are elucidated. © 2016, Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg.