TiAl alloy has the advantages of low density, high specific stiffness, high specific strength, excellent high temperature mechanical properties, and has a broad application prospect in the aerospace field. However, due to the low room temperature plasticity, damage tolerance and machining properties of the alloy, the high manufacturing cost of the alloy limits its application field. The uniform and fine microstructure can significantly improve the room temperature ductility and machining properties of TiAl alloy. The metastable microstructure transformation, such as massive γM phase, martensite α′ phase and full B2 phase transformation, obtained by high temperature quenching and refined TiAl alloy microstructure were reviewed. In the tempering process, the decomposition of metastable microstructure can refine the alloy microstructure. The higher the subcooling degree of metastable microstructure, the higher the nucleation rate of precipitated phase, and the grain refinement effect is more significant. The problems existing in various methods of microstructure thinning and their effects on mechanical properties were discussed.