A fine bonded interface is essential for the property of metal matrix composites. In this paper, an innovative method to strengthen boron carbide reinforced aluminum composites (B₄C/Al composites) was studied by liquid stirring technology. The effect of interfacial reaction on the microstructure and mechanical behavior of B₄C/Al composites was revealed by addition of Ti. Through B₄C-Al melt interfacial reaction, Ti element strongly enriched at the interface. A dense and continuous nanoscale layer of TiB₂ was formed on the surface of B₄C particles. Interfacial modification was achieved by interfacial reaction. Due to the formation of TiB₂ layer with good wettability and bonding, interfacial defects were eliminated. Increasing the degree of reaction, such as Ti content and reaction time, the strength of B₄C/Al composites was gradually improved. Severe interfacial reaction introduced lots of nano-scale TiB₂crystals into the matrix, which as in situ second reinforcement also improved the strength of B₄C/Al composites. Fracture behavior of B₄C/Al composites with different interfacial modification was discussed at last.