Abstract: The departure from nucleate boiling ratio (DNBR) design limit is the basis of nuclear reactor safety analysis. More safety margin could be clarified through the suitable method. In this paper, the RTDP and MSG methods which were used in nuclear power plant (NPP) design were compared. The basic principle and calculation procedure were described. The DNBR design limits were respectively calculated for Ling’ao NPP. The statistical principle of the two methods is different, but they obtain the similar result of DNBR design limit under the same condition and using the same statistical input parameter. For the safety design, the determination of method depends on the application.