Core catcher is a commonly used measure to alleviate severe accident in third-generation nuclear power plants. In the new type domestic core catcher designed by China Nuclear Power Engineering Company, the designers innovatively proposed a design scheme to improve the cooling rate of the corium by built-in cooling pipe. Based on the design of core catcher installed in Jiangsu Tianwan nuclear power plant, a numerical simulation model was established by FLUENT software to study the long-term cooling process of molten material in the crucible type core catcher, and the contribution of built-in cooling pipe to accelerate the process of severe accident mitigation was also discussed. The calculation results show that the oxide in the crucible type core catcher will freeze from outside to inside, and the formed crust will keep the decay heat, thus increase the time required to cool all the corium. The built-in cooling pipe can provide additional cold source for the internal area, thus improving the cooling speed of the corium and accelerating the mitigation process of severe accident.