Future aerospace vehicle highpower servo actuator will widely use electric hydrostatic actuator (EHA).It is a high demand to carry out study of relevant design methods according to the vehicle performance specification.Considering its multidisciplinary coupling characteristics,it is necessary to conduct system preliminary design after the EHA architecture design,including determining the main design parameters and component selection,which is the foundation of the following detailed design of subsystem.The system preliminary design method was studied,which divided into three parts: static characteristic design,dynamic characteristic design and design result verification.Based on AMESim simulation software,the design efficiency and reliability are improved at the same time.This method can provide a reference for EHA product development.