Abstract: Ships usually produce a certain degree of vacuum in the ballast tank to inject or discharge seawater through the sea piping system to realize the ship attitude control, in which the sea valve is an important device connecting the internal seawater piping system of the ship and the outside world. However, the existing sea valve has some problems, such as a large flow resistance coefficient and high noise pressure level. This paper proposes to use the deflector structure to reduce the internal flow resistance and noise of the sea valve, using Fluent software and LMS virtual lab software to numerically simulate the flow field and noise in the sea valve without and with different sizes of the deflectors, and the distribution of velocity, velocity streamlines, pressure, turbulent kinetic energy and noise pressure level in the flow field of the sea valve is also studied. Finally, the results of the numerical simulation are compared and analyzed, and the optimal results are obtained. The results show that adding a deflector plate inside the sea valve can effectively reduce the pressure drop of the sea valve, improve the flow field, and reduce the flow-induced noise. At the same time, a comparative analysis of sea valves with different thicknesses of deflector plates is carried out, and it is found that the performance of the sea valve with 8 mm thick deflector plates is relatively optimal. Through the design of different structure deflectors in the sea valve and the simulation calculation, the rationality of the improvement measures is verified, and the reference is provided for the optimization of the sea valve. By comparing the calculation results of different deflector structure schemes of sea valves, the rationality of the improvement measures is verified, and reference is provided for the optimization of the inner flow path of the sea valve.