As-cast 30Cr2Ni4MoV steel was researched quantificationally to obtain the distribution and pattern of the microcosmic defect. By means of finite element simulation and experiment research, porosity consolidating and relative density evolution of as-cast 30Cr2Ni4MoV steel were investigated for a FM stretching process at a constant strain rate 0.001s-1. The studied parameters included three temperatures (800°C, 1000°C, 1250°C) and three deforming passes(1,2,3) and three friction factors(0.3,0.5,0.7), which bracketed the parameters that were used during most primary break-down processes. Temperature had an obvious effect on the porosity consolidating, but friction factor had no effect on the ultimate soundness nearly. When beginning temperature was 1250°C and heat exchanged considered, initial porosity can be eliminated after the accumulated effective strain reached 1.0 at least. The residual defect of the wrought material at different strain lever was compared to the initial defect of as-cast material and found to be somewhat reduced. The impact toughness of the wrought material at different strain lever was also compared to the as-cast material and found to be obvious improved. The difference in these behaviors between as-cast and wrought material could be attributed to the healing of the porosity defect and the enhancement of the soundness at a certain extent.