Abstract: In hydroelectrical simulation the key model is that of hydroturbine governor. Discussing the way to develop the nonlinear mathematic model of the governor in the hydroelectrical simulation system and improve it, the phased analyzing/fitting method is introduced in modeling process to deduce the mathematical models of governor start-up and load rejection so as to solve the problems of overspeed starting and nonconvergent vibration during load rejection. According to the performance evaluation of the version 2.0/3.0 of the hydroelectric simulation system, the model developed is proved superior to the conventional one and running well during the simulation done in Fengman Hydropower Station.