Abstract: Based on the requirements of latest codes and rules and the research achievements of US NRC, the analysis methodology for reactor pressure vessel (RPV) structure integrity under pressurized thermal shock (PTS) was presented. For a series of PTS transients, the thermal-hydraulic responses of a typical conventional PWR were calculated with the thermal-hydraulic system analysis program RELAP5, and fracture mechanics analyses of the RPV model were calculated with the finite element analysis software ANSYS. Furthermore, the risk assessment was performed under these PTS transients, and the effect of RPV material embrittlement was studied. The analyses indicate that the surface flaws and the flaws close to the interior surface of the RPV are more vulnerable to produce crack initiation than those deeper in the RPV wall. Besides, axial flaws are more vulnerable to produce crack initiation than circumferential flaws under the same conditions, and axial flaws are much more likely than circumferential flaws to propagate through the RPV wall in medium and large diameter breaks.