Compared with the traditional technology of vanadium extraction from vanadium slag, a new process of classified roasting-acid leaching is researched in this study. Based on the theoretical analysis on the principle of calcified roasting process, the roasting mechanism and the effect of three kinds of calcification agents (CaSO4, CaCO3 and CaO) on vanadium extraction in the calcified roasting and acid leaching processes are investigated in which high-vanadium slag is used as raw material. Research results show that the leaching ratio of vanadium increases with the increasing of roasting temperature when the temperature is lower than 1 450 K. The leaching ratio reaches maximum at 1 450 K, and then comes down. The best calcification agent composition is 100% CaSO4. By controlling the experimental conditions, the leaching ratio of vanadium in high-vanadium slag can reach 93.53%.