Abstract: The loss of coolant accident (LOCA) research of the supercritical water-cooled reactor (SCWR) is the key and difficult task for the safety analysis, and especially the research of the depressurization process of the pressure vessel is of crucial importance. The reactor pressure vessel was simplified and mathematical physics models were established in this study. A transient calculating code was developed. A comparison between experimental and calculated results for supercritical carbon dioxide was carried out. It is showed that the predicted results by codes are in good agreement with the experimental data. The depressurization process was analyzed by the verified code. The influences of different initial conditions, breach areas and heating powers on the depressurization process were discussed. The results show that the models established in this study can simulate the depressurization process from supercritical to subcritical state, and the calculating results may provide a theoretical basis for accident analysis of the SCWR.