Abstract： A bow thruster is the main research object. In order to obtain the initial data for the optimization of structural design, the flow field in the tunnel is numerically simulated through solving the unsteady Reynoldsaveraged NavierStokes (RANS) equations by the finite volume method and the analysis on the pressure fluctuation is carried out. The numerical results agree very well with the measured data of the model test. The pressure fluctuation is concentrated in small area near the blade tip. By comparing the pressure fluctuation on the tunnel wall under different flow directions, it is found that the pressure fluctuation reaches the minimum and maximum value respectively when the flow is coming from the front and the back of the ship. Furthermore, the study shows that the fluctuating pressure is related to the complexity of the flow field. The smoother the flow is, the smaller the fluctuating pressure becomes, and vice versa. Due to the high precision of the numerical simulation, the results obtained in the paper are of great reference value for optimal design of structures. Therefore, the study is of profound practical significance in engineering.