The heat of linear motor affects normal operation of the motor seriously. The accurate computation of temperature field will provide a theoretical foundation for the design and control of linear motor. A three-dimension thermal model of linear motor is created in this paper. As the linear motor is running back and forth in an adjustable speed, the mean effective current of linear motor can be calculated firstly. On this basis, the calorific value of windings is calculated. The heat transfer coefficient of linear motor in each surface is calculated when the linear motor is running in a low speed. Then the steady state temperature field of the flat linear motor is simulated by the finite element software ansys.