The problems of harmonics and the heat of ventilator-driving induction motor(VDIM) are quite large when operating under the frequency conversion control system. The cooling structure of VDIM is usually complex. In order to investigate the rule of the temperature distribution of VDIM , 4 500 kW motor is taken as an investigated example. Based on the electromagnetic theory and heat transfer theory, a three dimensional of ventilation-cooling physical model is built to simulate the electromagnetic field in the motor under rated operating condition using the finite-element volume method, non-uniformly distributive loss (NDL) is mapped to the temperature field in the type of heat source, and by bi-direction coupling between electromagnetic field and temperature field, Calculating the distribution regularity of parts exactly. Besides in order to compare clearly, the same operation conditions are simulated using homogeneous distribution volume heat sources (HDVHS). By comparing with the test result of VDIM, the result of NDL is much more approach to the true data than HDVHS, which indicate that the method of Bi-direction coupling is more scientific.