This paper describes thermal modeling for three temperature rise parts of capacitor discharge impulse magnetizer. As the detailed thermal characteristics of capacitor discharge impulse magnetizer can be obtained, the efficient design of magnetizer which produce desired magnet will be possible using our thermal modeling. The thermal modeling method of magnetizing fixture resistor uses multi-lumped model with equivalent thermal resistance and thermal capacitance. Also, the thermal modeling method of semiconductor devices, i.e., discharging thyristor and recovery diode, uses the analog behavioral SPICE model . The reliable results are obtained by using iron core fixture (stator magnet of car air-cleaner DC motor) coupled to a small-voltage magnetizer (charging voltage : 1200[V], capacitor bank : 4000[µF]).