Abstract: In this paper, a high-pressure water-jet manifold underwater net-washing machine was designed to solve the difficulty of net cleaning due to the inconvenient electric power supply during the offshore-cage aquaculture. The net-washing machine also overcomes the big head loss of the high-pressure storage net-washing machine. By hydraulic calculation, the parameters of the designed machine were: jet pressure p=5.57 MPa, nozzle diameter d = 2.6 mm, jet velocity v = 104.1 ms-1, jet power P = 12.3 kW, jet recoil F = 234.96 N. The marine cleaning experiment of the underwater net-washing machine showed that the overall performance of the machine reached the design requirements when the working pump met the required work pressure and flux.