Abstract: Since the architectural and functional advantages, composite structures have been widely applied in modern architectures.There are two main problems on the study of such structures: first is the calculation of damping when considering different materials; the other is the modification of low damping material after integral calculation using the integral damping ratio. Taking the high-rise building with steel tower on top for example, this paper suggests a construction method of non-classical damping matrix. The result shows the damping ratio based on this matrix can reflect the energy dissipation of 4 modals which describe the most of the main structure and the steel tower on top. Basing on the response spectrum method, this paper deduced the inaccuracy of the steel tower’s result when calculation on the integral damping ratio. According to the inaccuracy, this paper suggests a modification formula. The comparison with the accurate result shows the modification factor obtained by this formula has certain reference value