Abstract: The effect of alloying element vanadium on the thermodynamic equilibrium phases and the transformation temperatures A₃ and A₄ of T122 ferritic heat resistant steel were studied by Thermo-Calc software. The results show that the main precipitated phases in T122 steel are M₂₃C₆, MX and Laves phases. When the mass fraction of vanadium is less than 0.15%, a little Z-phase precipitates, and the content of Z-phase linearly decreases with increasing vanadium content. When the mass fraction of vanadium is more than 0.28%, two different types of MX precipitate. With increasing vanadium content, the proportion of MN phase decreases, but the proportion of M(C, N) increases. The effect of vanadium content on M₂₃C₆ and Laves phases is extremely limited. As a closed austenite region element, the transformation region between ferrite and austenite becomes small with the increase in vanadium content.