The invention discloses a generator excitation system based on phasor measurement and a parameter estimation method of a speed control system. The method is based on the unscented Kalman filter algorithm. The excitation voltage and mechanical torque are used as state quantities. The input data of a model is obtained by a phasor measurement unit, and the parameters of the synchronous generator excitation system and the speed control system are estimated. Compared to other estimation methods, the parameter estimation method of speed control system can achieve fast estimation, and estimate all mechanical parameters, speed and voltage controller parameters by measuring the output power, current phasor and voltage phasor of the machine. At the same time, the method is further applicable to different noise levels and different initial operating state environments.