The research achievements and status of dynamic characteristics of electro-hydraulic servo system were reviewed in recent years, and its future development trends were analyzed and expected. It was proposed that introducing the modern nonlinear vibration theory into electro-hydraulic servo system, and using the nonlinear dynamics theory to reveal the essence and mechanism of dynamic process of servo system. It was of great significance in implementation of condition monitoring and intelligent fault diagnosis to system, which has broad application prospects in science and engineering.