In this paper, modeling and identification of the excitation system in the thermal unit #3 of Touss power plant in Iran is presented. Two approaches of modeling, i.e. analytical and experimental modeling are used. In the analytical method, first, using the documents and circuit diagrams in the power station, a block-diagram for excitation system was suggested, then based on the extracted block diagram, a test procedure was defined and performed. The input output data corresponding to each block was obtained through the field tests. Time domain data at proper inputs and outputs associated with the model was recorded by a16_bit data acquisition system. In these approaches, the only nonlinearities considered in the block diagram are the limits. The other nonlinearities are reflected in the change of parameters in the linear transfer functions at different operating conditions. The simulation results and their comparison, show the good accuracy of derived models.