Stay cables of cross-sea cable-stayed bridges will generate self-excited vibrations in non-extreme wind environments. Based on technologies of modern monitoring and data analysis，the digital features of the self-excited vibration of the stay cable can be captured immediately，and the real-time performance of dynamics about stay cables can be reflected accordingly. According to features of commonality in the long-term monitoring data of vibrating acceleration of stay cables from a main channel cable-stayed bridge of a cross-sea bridge，an automatic extraction method for the non-stationary sections of wind-induced self-excited vibration of the stay cable is proposed based on the vibrating acceleration time series signal’s Gaussian mixture model of the upper envelope and the power spectrum of the frequency domain. The strategies，that identify the dominant frequency based on the non-stationary time series of self-excited vibration，then identify the damping ratio using the data of the last descent section after band-pass filtering，are proposed. By the proposed strategies，the interference on the damping ratio identification from energy brought by the natural excitation of the ambient wind in the ascent sections of the vibration amplitude is excluded. Based on the identified results of dominant frequency-damping ratio in the non-stationary sections of the self-excited vibration，data clusters of the modal frequency-damping ratio corresponding to each order of the vibrating mode are obtained by clustering the frequency values. According to the discrete and skewed characteristics of the damping ratio data，the statistical law of using the eμ of log-normal distribution model and the quantile value of its cumulative distribution function to describe damping ratio of stay cables is proposed. The frequency centroid of each cluster，as well as the probability characteristic parameter of damping ratio are used as indicators to represent the current state of the dynamic performance of stay cables. The main conclusions for the background engineering include： the signal of vibrating acceleration of stay cables on the bridge has strong noise and large interference，they must be eliminated in the analysis of dynamic characteristic； the amplitude maximum of the acceleration of the self-excited vibration of the bridge’s stay cable has exceeded 3000 mm/s²，the vibration amplitude is large； the average level of the damping ratio of the bridge’s stay cable is about 0.03%，which is lower than the recommended value of the design code.