Abstract: Thermal expansion molding process is expected to be integrated to form various foam sandwich composites. The expandable epoxy foam prepreg with an initial thickness of 1 mm was selected, and four kinds of foam sandwich panels with different thicknesses were prepared by controlling the mold cavity size and different molding pressures. The impact energies of 10 J and 42 J were used to study the effects of thermal expansion process and core thickness on the low-velocity impact properties of foam sandwich composites. The damage patterns of different specimens were investigated by ABAQUS finite element analysis, ultrasonic C-scan and the test data. Compression after impact tests were conducted to investigate the damage tolerance of different specimens. The results show that the foam core with higher expansion rate produces lower expansion force, and the impact strength of the foam sandwich board is reduced, but the structure has better energy absorption effect. Both high impact energy and low strength foam cores lead to higher damage degree of the skin. The compression strength decay rate of the sample at 10 J impact energy is 8.2%, and the compression strength decay rate of the sample at 42 J impact energy is 38.2%. The forming pressure and the thickness of the core have little effect on the damage tolerance of the foam sandwich plate. The high designability of structural and impact resistance properties of foam sandwich composites formed by thermal expansion process was determined.