Abstract: Deciding the internal pressure probability distribution of the fuel rod is a fundamental work in the DNB propagation analysis using Monte Carlo method. The traditional parametric method is used to assume that the internal pressure probability of all rods can be characterized by a normal distribution. But this is not always the case, sometimes there is far more differences between normal distribution and the real one. However, a new method, the non-parametric method was used in the treatment of the rod internal pressure data because of its applicability anywhere and good precision in the case of large samples, and the results show that it is more conservative to use non-parametric method than parametric method in DNB propagation analysis.