In order to predict occurrence of cracks of heavy forging equipment or accessories during hot forming, the high-temperature fracture behaviors of No. 50 steel were investigated by using the experimental thermodynamic method. The results show that the critical fracture strain is a function of the temperature and strain rate. Based on these results and the theory of damage mechanics, a ductile criterion was proposed, which could predict the occurrence of cracks. Besides, the accuracy of the proposed criterion was verified by conducting upsetting tests with different deformations and the corresponding simulation. Additionally, the applicability of the proposed criterion was investigated by implanting the criterion and various uncoupled criteria into simulation. The result shows that the proposed criterion can best predict the occurrence and location of cracks.