Cold-rolled Ti/Al laminated composites were annealed at 675~750 °C for different time with superfluous Ti and Al, and the interfacial microstructure evolution in Ti/Al laminated composites during annealing was investigated. The results indicate that the interfacial layer between Ti and Al consists of two sub-layers: a compact TiAl₃ sub-layer with the microstructure of many randomly oriented cracks filled with Al, and a granular TiAl₃ sub-layer with the microstructure of granular particles distributed in Al matrix. The thickness of the compact TiAl₃ sub-layer is stable at different annealing temperatures for different durations, but the thickness of the granular sub-layer increases with increasing the annealing temperature and duration. Furthermore, the average volume fraction of TiAl₃ phase in the interfacial layer at different temperatures decreases with increasing the duration. A reaction diffusion model, in which the TiAl₃ phase is regarded as the result of diffusion and chemical reaction, was established to evaluate the formation mechanism of the interfacial layer. Additionally, the dissolution of TiAl₃ phase into liquid Al was considered in the model. The calculated results indicate that the formation of TiAl₃ phase is governed by the chemical reaction, and the equivalent thickness of TiAl₃ phase in the interfacial layer obeys a linear relationship with annealing time, which is attributed to the rapid diffusion of Ti and Al atoms through the thin TiAl₃ compact sub-layer.