This paper proposes a thermal-electrical coupled model for silicon carbide traction inverter design. An electrical inverter model is coupled with a Cauer thermal network in PLECS/Simulink environment. The thermal network parameters are calculated using a simplified heat transfer method which can capture the heat transfer in the solid layers and the actual coolant flow. The design target is a silicon carbide inverter with a 100 kVA peak power. Computational fluid dynamics simulations and finite element analysis are conducted to validate the model. The comparative studies demonstrate that this model has a satisfactory accuracy across a wide range of operation conditions. Finally, this model is applied in characterizing the performance of the prototype inverter. After optimization, this SiC inverter shows an overall efficiency high than 99%.