Net clogging by attached organisms is one of the serious problems in deep sea aquaculture cage. How to realize the safe and efficient cleaning of cage is an urgent problem. In this paper, the structure of cage underwater cleaning robot was studied，and cavitating jet technology was used to clean the attachment on the surface of cage. The cavitation flow field inside the nozzle was simulated numerically by FLUENT software according to the underwater cleaning condition of the cage. The distribution of velocity field and vapor volume fraction near the nozzle was obtained by means of mixture model, cavitation model and Realizable Ƙ - ε turbulence model. The influence of nozzle inlet pressure and cleaning depth on cavitation effect of cavitating jet was also studied. The results show that the cavitation mainly occurs on the wall of the nozzle expansion section. Increasing the nozzle inlet pressure can improve the jet speed and high-speed flow range, and effectively improve the cavitation intensity, so as to enhance the cleaning strike force. However, with the increase of water depth, cavitation will be weakened. The results can provide a theoretical reference for the application of cavitating jet in aquaculture cage.