Thermal field analysis for permanent magnet type retarder fin is an issue for its kernel design. A weakly coupled phenomena between magnetic and temperature fields occurs in retarder. Eddy current losses are inner thermogenesis of temperature field governing equations. Temperature rising tends to increase resistivity and decrease permeability, causing variety of eddy current losses. A coupled thermal-magnetic fields mathematic model with multi-factor effects was established. Thermal-magnetic field's model was calculated via ANSYS package and APDL algorithm method. At the same time, calculations of coupled algorithms and local as well as global convergence issues were discussed. Temperature distributions of cross section and axial direction were obtained. The accuracy of the calculation model was finally verified through experimental data and numerical results.