Fan nozzle is an important part of high pressure water descaling system, and its internal structure parameters directly affect the performance of jet. The nozzle flow field was analyzed by using fluid simulation software FLUENT, and the nozzle exit diameter, cone section contraction angle and exit contraction angle were selected as reference factors. The jet impact force was used as evaluation index, and the nozzle structure parameters were optimized by response surface method. The results show that the velocity distribution of the internal flow field is affected by the single factor of the diameter of the outlet section and the conical contraction angle, but the flow rate of the nozzle is little affected. The pressure drop of nozzle is affected by the change of the diameter of outlet section and the contraction angle of nozzle outlet, and the influence of the contraction angle of nozzle conical section on the pressure drop is negligible. When the diameter of the outlet section is 3.15 mm, the taper shrinking angle is 26.17°, and the outlet shrinking angle is 40.93°, it is found that the nozzle striking force is increased from the original 94.91 N to the optimized 143 N by establishing the outflow field and applying the gas-liquid two-phase flow model simulation calculation. The research results provide theoretical guidance for optimizing nozzle structure to enhance jet impact force.