Meta-biomaterials are applied to orthopedic implants to avoid stress shielding effects; however, there is no reason for the yield strength to be comparable to that of human bone. In this study, a composite unit cell was designed by combining the positive Poisson's ratio (PPR) and negative Poisson's ratio (NPR) unit cells, inspired by the second-phase strengthening theory. The purpose was to increase the strength while maintaining the elastic modulus. All structures were successfully fabricated from Ti-6Al-4V via selective laser melting. The relative density is between 0.08 and 0.24, which falls within the optimal range for bone growth. Mechanical tests indicated that the center of the inclined rod fractured in a stepwise fracture mode, which was consistent with the predictions of the Johnson–Cook model. The elastic modulus ranged from 0.652 ± 0.016 to 5.172 ± 0.021 GPa, and the yield strength varied from 10.62 ± 0.112 to 87.158 ± 2.215 MPa. An improved Gibson–Ashby law was proposed to facilitate the design of gradient structures. When the re-entrant angle was 40°, a hybrid body-centered cubic NPR structure was formed, resulting in a significant improvement in the mechanical properties. Importantly, the yield strength of the proposed composite structures increased by 43.23%, and the compression strength increased by 44.70% under the same elastic modulus. The strengthening mechanism has been proven to apply to other bending-dominated structures. Overall, this imparts unprecedented mechanical performance to auxetic meta-biomaterials and provides insights into improving the reported porous structures.