With the help of finite element method computing, the formation of metallurgical defects, such as hot tear, porosity etc was analyzed and the process of reducing the defects was verified in the paper. We found that the hot tear and porosity in tooldie steel are caused by the pull stress engendered by cooling contract and insufficient feeding of liquid metal in local position in billet. The hot isostatic pressing temperature employed is 170 ℃，and forging processing temperature can reach 150 ℃, die steel exhibits a certain plasticity at these temperatures, the hot processing can close metallurgical defects inside of the material after the thermal processing of the high temperature and pressure. Forging and hot roll process are important method to decrease and eliminate the looseness and porosity in deposit of tooldie steel. Further, as compared with the Ar gas, for tool and die steel prepared by spray forming thermal processing with the N2, deposition green density can close to the theoretical density.