Abstract: The pressurized thermal shock (PTS) in the assessment of life extension of a nuclear power plant should be paid much attention to. For Chashma NPP No.1 unit, a complete CFD model for RPV and its internals was established. Coolant velocity and temperature fields in RPV were simulated during normal state, and the results are consistent with experimental data. The coolant thermal-hydraulic characteristics in the RPV nozzle and the downcomer under SGTR transient were also studied in detail. The results were compared with the calculation results by RELAP5 code, and the good agreement is achieved between them. The present research could be useful for the calculation and analysis in RPV aging management evaluation.