[en] Models of generating with the pressurized water reactor (PWR) have been developed for simulating. the plant dynamics under system disturbances. These models include power plant, energy sources, turbine, transmission system and control system such as Avr and govern and other local control devices. Simulink toolbox of Matlab software is used for simulations. The study is mainly based on the Bushehr Nuclear Power Plants (BNPP) parameters. Assuming that BNPP is connected to infinite bus with double tie line. Four cases are studied to examine the internal dynamic behavior of BNPP. First and second cases are used to load following studies in nuclear power plant. Another cases are used to study the dynamic behavior after short circuit fault and line outages in transmission systems. The results discussed in the thesis