This paper analyzed thermodynamic principle of preparation VC,VN and V(C,N) with V2O5 and C by carbon-heat reduction. The results show that synthesizing process includes phase change and the vanadium oxide is reduced gradually. And because of the reaction kinetics, there are no obvious boundaries between each reaction. There are two principles for V2O5 reducing by carbon thermal method. One reaction depends mainly on CO/CO2 gas-solid transmitted and another reaction depends mainly on the solid-solid reaction between carbon and vanadium oxide. But no matter what kind of mixing method, two kinds of reaction mechanism are also present in different degree. The reacting principle which is primary is depended on original mixed condition between V2O5 and C. It is propitious to reducing process by increasing temperature. The preparation of VC should be done at the condition with CO or vacuum.