Detailed thermal dynamics of high power IGBT modules are important information for the reliability analysis and thermal design of power electronic systems. However, the existing thermal models have their limits to correctly predict these complicated thermal behavior in the IGBTs: The typically used thermal model based on one-dimensional RC lumps have limits to provide temperature distributions inside the device, moreover some variable factors in the real-field applications like the cooling and heating conditions of the converter cannot be adapted. On the other hand, the more advanced three-dimensional thermal models based on Finite Element Method (FEM) need massive computations, which make the long-term thermal dynamics difficult to calculate. In this paper, a new lumped three-dimensional thermal model is proposed, which can easily be characterized from FEM simulations and can acquire the critical thermal distribution under long-term studies. Meanwhile the boundary conditions for the thermal analysis are modeled and included, which can be adapted to different real field applications of power electronic converters. Finally, the accuracy of the proposed thermal model is verified by FEM simulations and experimental results and shows a good agreement.