With the development of all electric technology, electric actuator is widely used in aerospace, military applications and other fields. The motor of rudder system requires high power density, high dynamic response and high reliability. Permanent magnet synchronous motor (PMSM) is widely used in the servo system of the actuator because of its simple structure, high torque density, high power density and high efficiency. High power density motor generally refers to high speed high power density motor and high torque high power density motor. For the actuator system, it is mainly high torque density motor, which can meet the high dynamic response performance in the process of frequent acceleration. There are many researches on high torque density motors at home and abroad, such as HTS motor, slotless cylindrical linear motor, transverse flux motor, switched reluctance motor and so on. Although the power density of this kind of motor is very high, its technical development is not mature enough and its reliability can not be guaranteed. In this paper, the rotating surface mounted permanent magnet synchronous motor is mainly used. The short-time high overload motor refers to the motor can output the instantaneous large overload under the short-time state at the constant speed to complete the predetermined action of the actuator. In recent years, the research of short-time high overload motor is increasing. Harbin University of technology, Tianjin University and so on have done a lot of work. There are many researches on the thermal aspects of short-time periodic working motor abroad. Generally speaking, scholars at home and abroad mainly focus on the analysis of high power density and temperature field, and lack of analysis and Research on how to improve the limited torque output capacity of the motor and the impact of the external environment on the short-time high overload motor. Based on the actual engineering background, this paper analyzes the influence of electromagnetic load on motor overload capacity. By analyzing the influence of ampere turns on the limit torque of PMSM, the number of turns in series of each phase winding of PMSM is optimized; the influence of overload multiple on the distribution of motor loss is analyzed; and the law of temperature rise of PMSM under different ambient temperatures, such as long-term working system, short-term periodic working system and short-term high overload working condition is analyzed by finite element method; the experiment is verified. The correctness of theoretical analysis.