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A method to identify such two important characteristic parameters of joint interfaces as fractal dimension and fractal roughness was given. The expression of normal total load in joint interface was modified. A joint interface was selected as an example in XHK5140 automatic tool-changing CNC vertical boring and milling machine tool on the basis of the experimental results about test specimen, the theoretical solutions for normal and tangential contact stiffness were verified in terms of qualitative comparison principle of resembling mode shape and quantitative comparison principle of natural frequencies. The theoretical mode shapes agreed well with the experimental results. The relative errors between the theoretical natural frequencies and the experimental ones are between -9% and 9%.