The forged knuckle is a kind of common drawing components that it is used in couplers of railway wagons. The product has big section change and complicated shape，so it is difficult to form and forge thin muscle. According to the characters of forged knuckles, the blocking process was designed for hammer forging, which was composed of twice die forging and twice trimming. Based on rigid and plastic FEM, the process of die forging for forged knuckles was simulated using Deform\|3D. The metal flowing rule of the process was revealed. The loads and the defects produced by die forging process were analyzed during the forming process of each step. A reliable reference theory was offered for optimizing forging process. The qualified rate of finished products was greatly increased through improving the forging process.