According to the requirements for the compact structure, large torque, fast response and the other performances of driving system in robot, a joint driving system based on electro-hydrostatic actuation (EHA) technology was proposed. Linear motor, pump and load were integrated to provide larger pressure, simple structure and smart configuration. From the analysis in the magnetic circuit, the electromagnetic piston pump model and its equivalent magnetic circuit were developed to describe the magnetic field and its effect caused by piston’s movement in electromagnetic piston pump. Based on character integrated in mechanical, electrical and hydraulic, the working process model of driving system was built to explore relations between load and system current. Simulation and experimental results show that the proposed system can supply the maximum load pressure of 2.5MPa, work stably at 0~2.4MPa, and reach 1.2MPa/s in pressure response. The proposed driving system can meet the requirements in the robot joint driving.