Abstract: During the serious accident of PWR nuclear power plants,such as a loss of coolant accident,the analysis of core decay heat transfer will be complicated.This paper is based on the hypothetical condition of a double-ended loop break of the Daya Bay M310 and uses simplified method to research the decay heat transfer, by which getting the simplified calculating formula of the temperature filed via the time variable.Meanwhile,the results of the calculation are compared with the results of ANSYS software to testify.The results have showed that the errors of calculations can be accepted when taking a simplified analytical method on a certain conditions.This simplified analytical method not only can be used for PWR,but is also available for the other types of reactors.