Abstract: A finite element model of in-mold melting diffusion of V9Cr4 high-vanadium alloy was established with ANSYS software, and then the temperature change at different spots in the high-vanadium alloy rod was simulated during solidification after casting 5CrNiMo alloy liquid. According to the simulation that the axial temperature of the alloy rod changed little, the three-dimensional diffusion of alloy elements was simplified to two-dimensional diffusion, and the mathematical model for vanadium content distribution along radial direction was established. The vanadium content along radial direction was calculated and was verified by experiments. The results show that the temperatures of the alloy rod were higher than its solidus temperature during casting, indicating the metallurgical bonding between the high-vanadium alloy and 5CrNiMo alloy. The diffusion time of vanadium was determined to be 810 s from the temperature distribution curve. This diffusion time was substituted into the mathematical model for vanadium content distribution and then the vanadium content at different spots was obtained. The relative errors between the calculated content and the testing results were less than 1%, indicating that the established finite element model of in-mold melting diffusion was accurate, and its simulation could be used to calculate the vanadium content distribution.