The paper presents the dynamic multivariable model of Nuclear Power Plant steam turbine. Nature of the processes occurring in a steam turbine causes a task of modeling it very difficult, especially when this model is intended to be used for on-line optimal process control (model based) over wide range of operating conditions caused by changing power demand. Particular property of developed model is that it enables calculations evaluated directly from the input to the output, including pressure drop at the stages. As the input, model takes opening degree of valve and steam properties: mass flow and pressure. Moreover, it allows access to many internal variables (besides input and output) describing processes within the turbine. The model is compared with the static steam turbine model and then verified by using archive data gained from researches within previous Polish Nuclear Power Programme. Presented case study concerns the WWER-440 steam turbine that was supposed to be used in Żarnowiec. Simulation carried out shows compliance of the static and dynamic models with the benchmark data, in a steady state conditions. Dynamic model also shows good behavior over the transient conditions.