A giant magnetostrictive actuator(GMA) used in servo valve was designed. Phase change materials was used to the temperature control of giant magnetostrictive materials(GMM). The heat source of the actuator and the latent heat of phase change materials filled in were analyzed theoretically, and the thermal characteristics of the actuator was studied using classical ANSYS, then the effect of phase change materials on the stability of the GMM rod temperature change under constant electric current was analyzed.