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• The multi-material FDM technique is utilized to fabricate the IPC structures. • The mechanical behavior of IPC structures is investigated by FEM and experiment. • The Gibson-Ashby model is used to evaluate property and deformation mechanism. • The property enhancement effect of IPC structures is analyzed quantitatively. The triple periodic minimal surface (TPMS) structures have received widespread attention due to their excellent mechanical properties, such as high specific strength and energy absorption. However, these structures are prone to suffering catastrophic damage due to stress concentration and shear deformation in actual loading environments, affecting their load-bearing performance. In this work, interpenetrating phase composite (IPC) structures were fabricated by filling thermoplastic polyurethane (TPU) as a soft material into the diamond minimal surface structure using the multi-material fused deposition modeling technique, and their mechanical behavior was investigated numerically and experimentally. The effects of topological types and volume fractions on the performance of IPC structures were investigated. It is shown that the IPC structure undergoes stretching-dominated deformation, and its strength and toughness are significantly improved compared to the TPMS structure. Due to the addition of a complementary phase structure made of TPU, stress concentration and shear failure are reduced. The global deformation of the IPC structure and stress distribution of the TPMS phase are more uniform, effectively protecting the entire structure from catastrophic failure. [ABSTRACT FROM AUTHOR]