Taking the UAV fire-fighting grenade cover as the research object, Moldflow software was used to compare and analyze the two gate design schemes from five aspects such as filling time, flow front temperature, welding line, air pockets, and warpage change of the fire-fighting grenade cover, to get the optimal gate scheme. The two cooling systems were analyzed by Moldflow analysis, and the optimal cooling system was obtained by comparing the parameters after analysis. After the numerical calculation of clamping force and mold flow analysis, the injection molding machine meeting the molding requirements was selected, and then the orthogonal test was used to optimize the process parameters, so as to reduce the volume shrinkage rate of the decorative cap. The overall temperature distribution of the plastic part and the shear rate and volume distribution were verified, and finally the optimized structure of the injection mold was obtained. The results show that the analysis of Moldflow software and the results of orthogonal test can improve the design efficiency and quality of the UAV fire-fighting grenade cover mold, and the optimized injection mold structure is reasonable and reliable, which can effectively reduce the cost of the trial mold to meet the production requirements, and provide a reference for the design of similar molds.