In order to explore the dependent relationship of modal damping ratio on wind speed dependence of long-span suspension bridges，a total of 3015 sets of acceleration samples，which were gathered by the Xihoumen Bridge Health Monitoring System，were used to identify the modal parameters at 7 sets of wind speeds by the NExT-ERA method，which combined the natural environment excitation technology with feature system realization algorithm. The wind speed dependent characteristics，probability distribution and confidence interval of the structural modal damping ratios were analyzed. The statistics parameters of modal damping ratio and their variations with wind speed were also discussed. It has been found that although the mode damping in horizontal direction was always greater than 1.0%，the minimum value of damping ratio in vertical and torsional direction at 95% confidence level might approach to 0.2% and 0.3% respectively at a specific wind speed. Besides，the change of wind speed had a significant impact on the mean value and deviation of the modal damping ratio of long-span suspension bridges. Under the same wind speed，the mean value and variance of modal damping ratio in torsional and lateral direction were significantly greater than vertical damping ratio. As the wind speed increased，the mean value and variance of vertical damping ratios gradually increased，and the mean value and variance of the torsional damping ratios decreased slightly，while the lateral damping ratios did not change too much. The modal damping ratios of the three directions of the structure under different wind speeds all followed the generalized extreme value distribution，but the wind speed would affect the tailing properties of the probability distribution of the vertical and torsional mode damping ratios of structures.