For bettering the power module's reliability, a thermal model that can predict the junction temperature of the chip is proposed. In the thermal model incorporating thermal diffusion angle, the heat conduction area is typically approximated as a circle when heat is transferred from the chip to the heat dissipation substrate. However, when the convective heat transfer area of the chip thermal model located near the outside of the module on the DBC can no longer be equivalent to a complete circle, large calculation errors arise, necessitating modification. In this paper, the traditional thermal model is used to model the module, and the outcome of the simulation is analyzed. This approach realizes the modification of the traditional thermal model by replacing the convective heat transfer area of the adjacent chip thermal model with the chip thermal model whose convective heat transfer area cannot be approximately equivalent to a complete circle. The universality of the approach is ultimately confirmed by different models.