Abstract: Taking a once-through steam generator designed by Babcock & Wilcox as the study object, a graphical model was established, based on the basic module of supporting platform APROS. On this basis, the steady-state and dynamic simulation were carried out under varying operating conditions. According to the results, the enthalpy of the primary inlet and the pressure of the secondary outlet had the greatest influence on its steady-state characteristics, and the temperature of the primary inlet had the greatest influence on its dynamic characteristics. The impact of the position and degree of the breakage on the operating characteristics of the once-through steam generator when the heat exchange tube ruptures was studied further. The results show that it has the largest influence on the operation of once-through steam generator when the rupture takes place in the position near by the primary side’s inlet. And the more the leakage mass flow, the more influence on the operation characteristics of the once-through steam generator.