Abstract: In this study, DOEL-2 nuclear power plant is used as the study object. The cosSyst code is used to model the DOEL-2 reactor system under the steam generator tube rupture（SGTR） accident. Comparing with the power plant data and RELAP5 simulation res ults, and evaluate the accuracy of the cosSyst code for SGTR accident prediction. The results show that the cosSyst code is capable to simulate the process of SGTR accident, and the major thermal hydraulic parameters of the primary system and the secondary side of the steam generator are fairly consistent with the power plant data. The cosSyst code is capable to predict and analyze SGTR transient accidents.