Abstract: Two characterization methods of fracture toughness of reactor pressure vessel (RPV) steels are briefly introduced. One is the Lower-Bound Curve based on the reference temperature of nil-ductility transition temperature (TNDT), another is the Master Curve based on reference temperature (T0). Typical statistical models of fracture toughness data are stated, to represent the scatter of these data. The failure probability of RPV at pressurized thermal shock (PTS) is calculated with different statistic models, based on a probability fracture mechanics (PFM) analysis program developed independently. The results may provide reference to establish the fracture toughness statistic model of homemade steels for RPV.