Abstract: Cr12MoV die steel was tested for strain induced crack opening (SICO) experiment at different deformation temperature (900, 1 000, 1 100, 1 150, 1 200 ℃) and deformation amount (10%-80%). The formation of surface crack was observed and the effect of deformation temperature and deformation amount on crack was analyzed. The results show that when the temperature was constant, cracks would appear only when Cr12MoV steel reached a certain amount of deformation. With the increase of deformation, the number of cracks increased. At different temperatures, Cr12MoV steel had different critical deformation. When the deformation was higher than the critical deformation, the number of cracks increased with the increase of deformation until the specimen cracked. The main reason for the specimen to cracking at low temperature was that many net carbides precipitated and weak areas formed at the grain boundary, leading to the specimen to cracking under a certain amount of deformation. The main reason for the specimen to cracking at high temperature was that the carbides gathered and grew up due to overheating, resulting in the stress concentration, which reduced the plastic and toughness of the material and led to cracking. The range of the best processing temperature for Cr12MoV steel obtained by SICO test and hot tensile test was same, both of which were 1 100-1 150 ℃, and 1 150 ℃ was the best forging temperature.