In order to study the optimal combination of molding process parameters for the upper cover of composite battery pack, for the upper cover of a new energy vehicle battery pack, firstly, four main process parameters in the molding process were selected, and nine sets of material-level orthogonal experiments were conducted to test and compare the tensile and bending properties of laminates. The results show that when the temperature is 150 ℃, the molding pressure is 10 MPa, the preheating time is 20 seconds, and the insulation time is 500 s, the comprehensive mechanical properties of the molded material are the best, with the tensile strength of 584.41 MPa and the flexural strength of 870.58 MPa. Secondly, the generalized Maxwell model parameters during the material molding were determined by relaxation property experiments of material, and the hyperworks molding simulation for the upper cover of battery pack was performed. Using the maximum equivalent stress as the criterion, the optimal process parameter combination was determined as the mold temperature of 150 ℃, the molding pressure of 10 MPa, the preheating time of 20 s and the holding time of 500 s, and the minimum value of maximum equivalent stress after molding was 210.5 MPa. Finally, the process parameter combination was verified. The result shows that the product meets the requirements of production and quality, indicating that this optimal parameter combination can be used for the mass production of the upper cover for composite material battery pack.