Abstract: The electro-hydraulic servo system has the advantages of fast response speed, large output power and good impact resistance, so it is widely used in the structural strength tests of aircrafts. However, due to the special physical structure and working principle, the electro-hydraulic servo system has complex nonlinearities, uncertainties and time-varying characteristics, which bring great challenges to dynamic modeling and controller design. Thus, in this paper, by analyzing the physical characteristics and working principle of each component of the system, the servo valve flow equation, the asymmetric hydraulic cylinder flow equation and the hydraulic cylinder force balance equation are established respectively. Subsequently, through a series of mathematical changes, the dynamic equations are transformed into the state space equations of the system, which facilitates the model-based controller design in the future work. Finally, the simulation platform of the system is built, and the PID controller is used for tracking control simulation tests. The test results demonstrate the effectiveness of the proposed dynamic modeling method for electro-hydraulic servo system.