Abstract: Servo-loop speed control system is an indispensable part of the hydraulic system. Transfer function method, by analyzing the dynastic characteristics of hydraulic system, is conventionally applied to establish mathematical model for a deeper understanding of system properties. A mixed modeling is applied by combing power bond graph modeling and transfer function to establish systematic mathematical model. Matlab software simulation is adopted to establish systematic mathematical model.Matlab software simulation is adopted to analyze the system performance. The research has positive effects on better understanding the system properties and design improvement.