The hardening mechanism of nitrided Fe-2.0Al-xV-0.2C（x ＝0.0-1.0）alloys which indicates prominent hardness and nitrided case depth was investigated. During pre-heat treatment, the addition of Al inhibited the growth of vanadium carbide precipitated in the matrix of Fe-2.0Al-xV-0.2C alloys. After nitriding, the hardness of nitrogen diffusion layer increased as the precipitation of vanadium carbonitrides which reacted from vanadium carbides. While Al became concentrated at the near-surface region with nitriding in Fe-2.0Al-0.2C alloy, the addition of V reduced the diffusion of Al and Al was uniformly distributed in the nitrided layer region to form AlN in Fe-2.0Al1.0V-0.2C alloy. The coexistence effect of Al and V for these alloys contributed to the precipitation hardening of V（C, N）and AlN in diffusion layer and the increase of nitrided case depth.