ElectroHydrostatic Actuator System (EHAS) is one of the key subsystems of more electric aircraft. Because of its compact structure, the heat transfer ability is poor, which influence the flight. Therefore, thermal characteristics research of EHA is very important. Simplified the structure of EHA whole processing and obtained the thermal characteristics analysis model, the thermal characteristics of EHA were received by using the finite element (FE) simulation software. Compared with the experimental results suggested that the analysis methods is accurate and structure optimization schemes were put forward. Through optimization modeling and simulation, the thermal characteristics of optimized model were obtained. The steady state thermal analysis maximum temperature of EHA optimized structure was reduced by 29.5% and the maximum temperature of transient analysis by 22.3%, as compared with the original model. The research provides a solution to analysis EHA thermal characteristics, which proposes an optimization and improved scheme for existing structure layout, to improve the thermal characteristic. Furthermore, the research is helpful for the development and design of new products.