Mg-Ti composite with bicontinuous phase structure was prepared by the additive manufacturing (AM) coupled with the melt infiltration. The effects of pore structure type and size parameters on the porosity and mechanical properties of AM-prepared Ti-6Al-4V (TC4) porous scaffold reinforcement were investigated. By adjusting the size parameters, both high porosity and appreciable compressive strength can be achieved for the scaffold. The strengthening effect of titanium alloy scaffold on the mechanical properties of Mg-Ti composite was investigated by analyzing the microstructure and interface bonding mechanism. Results show that the Mg-Ti composite has high compressive strength of 400 MPa, whereas its density is only 2.56 g·cm^-3, presenting the potential as lightweight structural materials. The strength of Mg-Ti composite is higher than that of raw Mg-9Al-1Zn (AZ91) alloy matrix by 51%. This enhancement is attributed to the tight metallurgical bonding interface between the scaffold and the matrix, which promotes the effec-tive transfer of load. Additionally, the mutual constraint effect caused by the bicontinuous phase structure and the fine crystal streng-thening caused by the ultra-fine α'-Ti martensite in TC4 scaffold also significantly contribute to the improvement of mechanical pro-perties. The investigation strategy in this research provides a nouveau path for the development of structural lightweight composites.