Abstract: A three-point bending finite element model of Primitive triply periodic minimal surface (P-TPMS) sandwich structure was established and verified by three-point bending experiments. The effects of cell size (8, 12, 24 mm), relative density of P-TPMS structure (0.15, 0.20, 0.25), and panel thickness (1.5, 2.0, 2.5 mm) on the ultimate load and bending stiffness of the sandwich structure were investigated by the established finite element model. The results show that the overall change trend of simulated force-displacement curves was basically consistent with experimental results, and the relative error of ultimate load was 5.7%, which verified the accuracy of the finite element model. The ultimate load of the sandwich structure first increased and then decreased with the increase of the cell size, reaching the maximum value under the cell size of 12 mm, which was 9.2% higher than that under cell size of 24 mm. With increasing cell size, the bending stiffness decreased. The bending stiffness under cell size of 8 mm was 23.9% higher than that under cell size of 24 mm. The ultimate load and bending stiffness of the sandwich structure increased with the increase of the relative density of P-TPMS structure or panel thickness. The ultimate load and bending stiffness under P-TPMS structure relative density of 0.25 were 91.4% and 78.1% higher than those under P-TPMS structure relative density of 0.15, respectively, and those under panel thickness of 2.5 mm were 34% and 38.7% higher than those under panel thickness of 1.5 mm, respectively.