Abstract: The interface of the spindle-tool holder is the most weakness structure in the system of spindle- tool holder. It affects the manufacturing efficiency and the surface quality of work piece. It is important to identify the dynamical contact parameters to evaluate the connectivity of the spindle-tool holder system. The paper advises a method to identify the dynamical contact parameters for spindle-tool holder interface based on frequency response functions. The least squares solution to solve model is used. With the spindle-tool holder system of BT40 as an example, it can get the frequency response functions through Ansys and identify the dynamical contact parameters for the spindle-tool holder interface. It can get the different stiffness on the different drawbar force and different position of the spindle-tool holder interface and the validation shows that identification of the dynamical contact parameters for spindle-tool holder interface with the proposed method is right. The research can provide a theoretical basis for the optimization of tool holder.