In the process of cage aquaculture, attachments on netting affect water exchange and normal growth of fish in cages. A rotating disc cage cleaning device was designed to solve the problem of attachments on netting. With the selected pump (rated flow QR = 30 L/min, rated pressure pR = 20 MPa), continuity equation and Bernoulli equation were applied for prototype test through hydraulic calculation and with flow velocity method to determine that the optimum nozzle diameter of the cleaning discs d = 0.6 mm, the jet velocity v = 196.41 m/s and the jet pressure p = 19.3 MPa. The computational fluid dynamics software FLUENT based on the finite volume method was used to carry out the numerical simulation analysis of the high pressure water jet field, and the maximum working distance between the cleaning discs and the netting was determined to be 10.3 mm; it was verified that the hydrodynamic parameters of this jet could be accurately calculated by using the Realizable ｋ-ε turbulence model. The results show that the designed cage cleaning device can meet the netting cleaning requirements, which provides references for the design and optimization of cage cleaning device.