The causes of mold cracking in use are: too low design strength, too small mold gap, too high material strength, too high mold stress, defects in the material itself, and too high heating temperature of heat treatment, which leads to coarse martensite grains, coarse fracture and low toughness and plasticity. The demoulding inclination of the die is too small, or slightly inverted, which leads to unfavorable material leakage of the die and excessive material storage, which causes the die to crack.