The mechanism of brittle fracture of hot-forged cast dies was discussed and the effective solutions were put forward. The brittle fracture of hot-forged cast dies was attributed to imperfection of materials and processes, which results in unstable lifespan. Through optimizing materials and processes, brittle fractures can be avoided. The early brittle fracture seldom occurs, which is resulted from abnormal heat treatment and operation. Impact fatigue fracture is the dominant pattern in brittle fractures of cast die which is caused by the fabrication defects, such as sand inclusion, micro-crack and thermal fatigue crack, which are taken as initiated crack to propagate to fracture.