At present, it is necessary for the calculation of the supplemental damping ratio of the aseismic structure to calculate the dynamic response of the structure and perform the iterative process. In addition, generally only the case where the excitation frequency is equal to the fundamental frequency of the structure is considered. Based on the nonlinear viscous damper, a calculation method that without calculating the structural dynamic response directly obtains the structural supplemental damping ratio based on structural characteristics, excitation frequency and damper parameters is proposed. Firstly, several frequently used methods for calculating supplemental damping ratio are analyzed. Then, the calculation formula of the supplemental damping ratio for the excitation frequency equals to the fundamental frequency of the structure, and without calculating the structural dynamic response and the iterative process is deduced. By studying on the influence of the excitation frequency on the calculation of the supplemental damping ratio for different damping indexes, a simplified calculation formula for supplemental damping ratio in the case of non-resonance is proposed. On this basis, taking response spectrum average period as the excitation frequency of the ground motion, a simplified calculation method of the supplemental damping ratio considering the excitation frequency and no need to calculate the structural dynamic response is given. Finally, the accuracy of the proposed method is verified by comparing the results of the example with the nonlinear time history analysis. The calculation of the additional damping ratio is the core of the structural damping analysis. The research in this paper presents a simpler and more accurate method for the calculation of the additional damping ratio.