The resin matrix composite materials with foam-core sandwich structures are widely used in the aviation industry, and the vacuum assisted resin infusion process can effectively reduce manufacturing costs. During the liquid molding process of sandwich structures composite materials, the incorrect flow behavior of resin during impregnation of the preforms can lead to defects such as voids and dry spots. To improve the product quality of foam-core sandwich structure composites, it is necessary to optimize the flow behavior of the resin during the molding process. In this study, the finite element method is used to simulate the impregnation process of preforms with different pre-treatment methods of foamcore material. The mechanical analysis was performed on the solidified sandwich structures composite panels. The results indicate that perforating the foam-core material is a more effective pretreatment method.