The computer program to simulate steam and power conversion system (SPCS) of nuclear power plant is developed to analyze various kinds of the SPCS transient. The major components for simulation are steam generator, main steam line, high and low pressure turbine, steam chest per turbine, separator, condenser and reheater. The feedwater line is modeled by feedwater pump and condensate pump. Steam generator water level and steam dump control systems are modeled. As numerical methods the semi-implicit scheme and the fully-implicit scheme are considered and tested. It is found that the fully-implicit scheme is much more efficient as compared with the semiimplicit scheme. To achieve real time simulation, the fully-implicit scheme with the Newton-Raphson method, to solve non-linear equations, is applied to a computer porgram.