Abstract: Aiming to mitigate impact of the uncertain boundary conditions setting on the underwater radiated noise calculation, the numerical prediction method of calculating the underwater radiated noise of a waterjet by the one-step boundary element method was explored. First, the transient flow field of the waterjet was calculated on the basis of Detached Eddy Simulation(DES), and the pressure fluctuations were transformed to the pulsant source with computational acoustic software. Next, taking the pulsant source as the radiant source, the underwater radiated noise of the waterjet was numerically predicted by the one-step boundary element method. The results show that the underwater radiated noise of a waterjet can be obtained by using the one-step boundary element method, which gives a more procise prodiction.