To solve the transient calculation of temperature field problem caused by unstable heating of the motor under complex working conditions, a two-dimensional coupling model of electromagnetic field and temperature field was established according to the law of unstable heat. Based on the structural characteristics of small type asynchronous motor, the structural parameters, boundary condition parameters, electrical and thermal physical parameters calculation, equivalent and configuration of the electromagnetic field-thermal field two-dimensional model were performed. According to the law of heating variation under complex working conditions, the coupling frequency and heat source coupling mode were designed, and the relevant parameters were calculated and configured. The transient temperature field calculation of the motor under unstable load was realized, and the actual maximum temperature distribution of each part of the motor was investigated. The temperature rise experiment was carried out through the scheme design and construction of the experimental platform. The simulation and experimental results of the transient temperature field of the motor showed that the rationality of parameters equivalence of the two-dimensional model and multi-field coupling method could accurately calculate the full transient temperature field of the motor under complex conditions.