Abstract: The feed-water heater is one of the major equipments in the secondary loop of nuclear power plant (NPP), and its behavior has an important influence on the safe and economical operation of NPP. The research on the behavior of feed-water heater by means of modeling and simulation can provide important theoretical basis for its design and operation. In this paper, the distributed parameter dynamic models of NPP feed-water heater were established, in which the nearly separated model was used to deal with two-phase flow. By simulating the behavior of actual NPP feed-water heaters under various operating conditions and comparing the differences between the simulation values and the actual values, the accuracy of the simulation models was proven to be higher than that of existing models.