The peritectic phase transition in traditional TiAl alloys during the casting process often leads to issues such as composition segregation and coarse microstructures, resulting in poor plasticity and significant anisotropy, which significantly affects the performance of TiAl alloys. To gain a deeper understanding of the peritectic phase transition process and further control the microstructure, a multiphase-field model was developed to describe the peritectic phase transition in TiAl alloys. By incorporating quantitative input of multiphase free energy, effectively handling multiphase interfaces, considering anti-trapping current, and a simplified calculation strategy for the virtual phase composition at phase interfaces, the peritectic phase transition process of Ti-45Al (at. %) alloy has been investigated. The focus is on studying the influence of undercooling on microstructural evolution during peritectic phase transition. Research has shown that during the peritectic reaction process, α grows rapidly along the β/L interface. Considering the difference in the growth rates of the α phase towards the L and β phases, asymmetry is observed in the growth of the α plate. Moreover, the peritectic transformation process occurs under diffusion control, and the migration of the α/L and α/β interfaces follows the law of xij =Aij t1/2. As the degree of undercooling increases, the migration rates of both phase interfaces increase, especially the migration rate of the α/L interface, which significantly increases. At lower degrees of undercooling, phenomena such as remelting of the β phase can be observed at the front end of the α layer. After increasing the degree of undercooling, this remelting phenomenon gradually disappears, but the shape of the L/β/α triple-phase region remains unchanged. The shape of the triple-phase region is mainly determined by the balance between the interface energies (interfacial tension) and is independent of the differences in the interface migration rates.