Abstract: The impact toughness of hot-pressed 13MnNiMoR steel vessel heads was unqualified. By means of chemical composition analysis, mechanical property testing, metallographic examination, simulated heat treatment and so on, the significant decrease reasons of impact toughness of the hot-pressed 13MnNiMoR steel vessel heads were analyzed. The results show that:the cooling speed of thick vessel heads after normalization treatment was seriously insufficient, which led to the carbide precipitation along the ferrite grain boundaries, and then carbide grew up in the process of high-temperature tempering process; in the impact process, the vessel heads were easy to fracture at the position of carbide precipitation under the exogenic action, leading to the significant decrease and disqualification of impact toughness of the vessel heads.