Abstract: Calcification roasting process of vanadium slag is just currently situated at pilot stage of industrialization in China,while the recovery ratio of vanadium from vanadium slag is only 69.7%.It is not clear so far whether the calcification or leaching process leads to the low recovery ratio. This paper studied the factors influencing calcification ratio directly by XRD（X-ray diffraction） semi-quantitative method. Experimental results show that calcification ratio of vanadium slag increases with rise of CaO and V₂O₅ content while decreases with increase of temperature.Fe[Ⅲ]V[Ⅴ]O₄ can be formed at exorbitant temperatures leading to a decrease in calcium vanadate content of the product. A highest calcification ratio of 100% can be obtained at 790℃ for 8 h with material containing 50% of CaO,25% of V₂O₅,total 25% of Cr₂O₃,SiO₂,and Fe₂O₃.From SEM results,it indicates that block calcium vanadate possessing smooth surface is mixed with calcium chromate,ferric chromate,ferric vanadate,ferric oxide and silicates. The research proves that present low recovery ratio of vanadium is due to the low efficiency of leaching rather than calcination,which provides a new insight for the production.