Abstract: As a deformation mode of thin-walled metal tube, the internal inversion mode of circular tube over a circular die has good energy absorption characteristics. However, in all previous theoretical models, the curvature in the deformation area is assumed to be a constant value and few of them pay attention to the inversion force of the whole inversion process. The internal inversion process of 6063 aluminum tube is studied by experimental testing and finite element simulation, and the deformation characteristics of the internal inversion mode were discussed in detail. Based on the experimental and numerical results, the curvature is found to be varying in the deformation zone and the wall thickness has thickened. Then a novel theoretical model for the internal inversion mode is proposed based on the characteristics of the deformation mode for internal inversion process. Additionally, the novel theoretical model can predict the internal inversion force throughout the whole internal inversion process, enabling us to obtain theoretical results for both total energy absorption (EA) and specific energy absorption (SEA). Furthermore, upon comparison with the previous theoretical results, the current theoretical results exhibit a higher degree of both experimental and numerical results. Finally, the effects of tube wall thickness, tube average radius and die radius on crashworthiness indicators are theoretically investigated using the validated theoretical model. The results show that there exists an optimal die radius which minimizes the internal steady inversion force, the total energy absorption and the specific energy absorption. Increasing the wall thickness can significantly enhance all crashworthiness indicators. Augmenting the tube average radius can increase both the internal steady inversion force and the total energy absorption, while decrease the specific energy absorption. The novel inversion theoretical model provides a theoretical foundation for characterizing the internal inversion deformation mode and utilizing the internal inversion tube as an energy absorber.