Abstract: Referring to the chemical composition of 4Cr5Mo2V hot-work die steel, test steels with V mass fraction of 0, 0.55% and 0.9% were prepared, and surface ion nitriding treatment was carried out. The effect of V content on the microstructure and properties of hot-work die steel after nitriding was studied. The results show that the matrix structures of three test steels were all martensite, and the nitriding layer was mainly composed of white bright layer and diffusion layer. With increasing V content, the matrix structure of test steel was obviously refined, the distribution of white bright layer became continuous, and the thickness of diffusion layer first increased and then decreased. When the V content was 0.55wt%, the matrix structure was the finest and the diffusion layer was the thickest. Fine granular precipitates rich in C, N, Cr and V appeared in diffusion layer after added V. As the V content increased to 0.9wt%, the number of precipitates decreased and the size increased. The surface hardness and wear resistance of test steels increased first and then decreased with increasing V content. When the V content was 0.55wt%, the surface hardness was the highest, 1 287.3 HV, the friction coefficient was the lowest, 0.15, and the wear mechanism was abrasive wear.