The numerical thermal mechanical simulations of radial forging process of C45 steel stepped shaft in radial forging both with four dies and with two dies were carried out by Deform 3D. According to the effective plastic strain, mean stress and mean plastic strain distribution in the forging, the forging penetration efficiency (FPE) and the phenomena of deep sinkage in the end of forging were studied. The results show that the effective plastic strain in the center of the forging are always larger than zero, which means the forging being forged penetrated even with 10% draught per pass. The effect of dies number of radial forging on the effective plastic strain in the center of the billet is very similar and its difference is not larger enough. The mean stress in the center of the forging is proposed to describe hydrostatic pressure in the forging, so that the stress state in the center of the forging would be investigated. Both with two dies and four dies, all of the mean stress in the center of the forging are negative. There is compressive strain layer beneath the surface of the forging, while there is tensile strain core in the center of the forging, this can be used to explain the phenomena of deep sinkage in the end of forging. In addition, as the die number n increases, the radial forging axial feed rate v also increases in proportion, and the production rate increases too.