Abstract: Power electronic converters need to meet the requirements of high power density and high reliability, and the performance of the heat dissipation system is a key factor affecting their reliability. To address the insufficient accuracy of traditional thermal models in forced-air cooling systems, a calculation model of the thermal resistance and flow resistance of the heat sink was established, which realized the rapid calculation of the forced-air cooling heat dissipation process under the condition of multiple heat sources. Through finite element simulation verification, this calculation model can significantly improve the calculation efficiency while ensuring the calculation accuracy in a wide parameter range. Finally, the experiment verified that the model has good accuracy and engineering applicability, and can provide an effective theoretical basis for the optimization design of the air-cooling heat dissipation system.