Abstract: Nozzle is the main actuator of high pressure water jet system. By taking conical convergent nozzle used for descaling in mine main drainage pipelines as the research object, the fluid field of internal nozzle is simulated by Fluent software. Results of axial pressure，turbulent kinematic energy and velocity are obtained by simulation. Through analysis of the results, the optimum parameters of nozzle are verified. The results show that the contraction angle that is between 〖10〗^° and 〖20〗^° and the length﹣diameter aspect ratio that is equal to 2 are the best matching parameters. Nozzle which is designed on the basis of the optimum parameters has stable pressure gradient, the optimal jet velocity gradient and stability of fluid flow. The simulation results provide a theoretical basis for the structrual design of jet descaling nozzle.