The hot deformation behaviors of steel D2 in the range of 900 ℃ to 1 160 ℃ and strain rate range of 0.01 s~(-1) to 10 s~(-1) have been studied by using Processing Map developed on the basis of dynamic materials model.The efficiency of energy dissipation η is taken as a function of temperature and strain rate to obtain a Processing Map.In the Processing Map of steel D2,there are two zones of cracking susceptivity with high dissipation efficiency η of 46%and 63%respectively.One zone is in the range of 900 ℃ to 980 ℃ and the strain rate range of 0.01 s~(-1) to 0.06 s~(-1),and the other from1 140 ℃ to 1 160 ℃ and 8 s~(-1) to 10 s~(-1).The experiment proves that there are microstructural brittle transgranular fractures and macroscopic thermal cracks in the two zones respectively.The map also revealed that deformation in these two zones is of instable flowing,so these two zones should be avoided when choosing hot deformation conditions. The hot deformation behaviors of steel D2 in the range of 900 ℃ to 1 160 ℃ and strain rate range of 0.01 s ~ (-1) to 10 s ~ (-1) have been studied by using Processing Map developed on the basis of dynamic materials model. The efficiency of energy dissipation η is taken as a function of temperature and strain rate to obtain a Processing Map. The Processing Map of steel D2, there are two zones of cracking suscetivity with high dissipation efficiency η of 46% and 63 % respectively. One zone is in the range of 900 ° C to 980 ° C and the strain rate range of 0.01 s -1 to 0.06 s -1, and the other from1 140 ° C to 1 160 ° C and 8 s ~ (-1) to 10 s ~ (-1). The experiment proves that there are microstructural brittle transgranular fractures and macroscopic thermal cracks in the two zones respectively. Map also revealed that deformation in these two zones is of instable flowing, so these two zones should be avoided when choosing hot deformation conditions.