Abstract: In order to accurately obtain the dynamic parameters of the shrink-fit HSK holder-tool joint, a fractal theory based model to calculate the contact stiffness of the shrink-fit HSK holder-tool joint was proposed. The relationship between the normal contact force and the contact stiffness was deduced according to the Hertz contact theory and fractal geometry theory. Based on the finite element analysis, the contact force distribution of the shrink-fit HSK holder-tool joint was obtained. Considering the special contact form, a theoretical model for the contact stiffness of the shrink-fit HSK holder-tool joint was established. Through impact experiments, it can be found that the relative prediction error for the first order natural frequency based on this model is 0.48%, which verifies the effectiveness of the proposed model. The effect of radial interference, tool insertion length and rotational speed on contact behaviors between the shrink-fit HSK holder-tool joint was investigated. The results show that there are approximate linear proportional relationships between the radial interference, tool insertion length and the contact force and contact stiffness. Moreover, rotational speed weakens the contact effect of the joint, and the weakening effect is more obvious under high rotational speed conditions. These results can provide a theoretical basis for assembling and adopting the shrink-fit HSK holder-tool structures.