Abstract: Titanium alloy/steel diffusion bonded composite components had a broad application prospect in advanced aerospace manufacturing. Still, the brittle intermetallic compounds (IMCs) were the main reason for the deterioration of the joints. AlCoCrNiCuAg high-entropy powder interlayer with liquid phase separation was innovatively designed. By forming parts of the liquid phase, the deficiency of single plastic deformation on the microstructure and mechanical properties in the interface was reduced. The effect of bonding temperatures on the interfacial microstructure and mechanical properties was investigated. The typical interfacial microstructure of α-Ti + β-Ti/β-Ti/β-Ti + Ti(Fe,Ni) + Ti₂Ni/Ti(Fe,Ni)/TiFe₂ + χ-Fe₂Cr₅Ti₁₇/ χ-Fe₂Cr₅Ti₁₇ + λ-(Fe,Cr)₂Ti + α-Fe/γ-Fe was formed. With the bonding temperatures increased, the thickness of Ti(Fe, Ni) and α-Fe adjacent to the TiFe₂ reaction layer increased, and the defects at the interface (pores) during the bonding were reduced. The shear strength indicated an increasing trend under the synergistic action, and the highest shear strength reached 181 MPa at 1010 ℃ for 30 min. The high entropy powder interlayer inhibited the generation of TiFe₂ IMCs and promoted the formation of the (Fe, Ni) solid solution phase, achieving a sound bonding. Meanwhile, the defects such as pores were significantly reduced.