Damping in double chains suspension bridge is non-uniform, which leads to coupled motion equations in main coordinate system. Based on the complex damping theory to solve equivalent viscous damping ratio used to describe energy dissipation characteristics of non-classical damping system approximately, a method is proposed to analyze seismic response of double chains suspension bridge considering non-classical damping modified by measured value. Influence of different damping forms on seismic response of double chains suspension bridge is analyzed, considering classical damping and non-classical damping respectively, through an example of double chains suspension bridge. The analysis shows that non-classical damping has significant effect on seismic response, and response based on the classical damping model is not reliable to double chains suspension bridge. Non-classical damping model should be used in seismic analysis of double chains suspension bridge, however, the seismic response of non-classical damping system under the longitudinal or vertical seismic wave can be substituted approximately by the seismic response calculated according to damping ratio of concrete tower and steel stiffening girder respectively, which can simplify the calculation during preliminary analysis.