Electric-hydraulic actuators, with their many outstanding features, are widely used in automatic control systems for vehicle engines. A typical electric-hydraulic actuator consists of fast switching valves and plunger-type hydraulic cylinders. . In this article, we first investigate the theoretical properties of electric-hydraulic actuators and develop mathematical models. We then use simulation to analyze how different system parameters (e.g. the spool aperture of fast switching valve, the plunger area of the plunger-type hydraulic cylinders, and etc.) affect the response sensitivity of the system. Based on the simulation results, we propose a new design what can significantly improve the response sensitivity of electric-hydraulic actuators.