The invention discloses a thermodynamic system actual output constraint based power generator speed regulation system model and modeling. According to the system model, the output mechanical power of the power generator can be controlled in real time according to the system frequency, a given frequency reference value and a given power reference value based on the actual output constraint of the thermodynamic system, a valve action range and the inertia of a shafting system; the problem that the existing model is too complicated is overcome; the power generator speed regulation model with moderate fineness, relatively high engineering practicability and high reliability is established; the modeling method is simple to operate and suitable for the actual power grid; and the obtained model parameters are reliable and effective, so that the power generator speed regulation system model and modeling are of great significance to the stable operation of the electric power system.