Abstract: Offshore wind power structure bear complex environmental loads induced by wind and wave, over the life time. Dynamic characteristic is an important basis for the safety assessment of the offshore wind power structure. Based on in-situ test data of offshore wind power on composite bucket foundation in Rudong, Jiangsu Province, those structural modal parameters under different environmental excitations were identified, and the evolution law of dynamic characteristics of offshore wind power with environmental excitation and time were analyzed. The results show that the modal frequency and damping ratio of the offshore wind power obey the normal distribution, and show a certain degree of dispersion. The modal frequency and damping ratio in side-side direction is concentrated in the range of 0.308~0.315 Hz and 2.75~3.5%, respectively. Wind load is the key control load of wind power structure vibration characteristics. There is a negative correlation between modal frequency and wind speed, and a positive correlation between modal radial damping ratio and wind speed. With the increase of wind speed, the correlation coefficient increases slightly when the wind speed is greater than 7 m/s. The mode frequency shows a certain degree of degradation, and the degradation is mainly concentrated in the first 150 days of the test period, reflecting the decline in the constraint effect of the soil on the bucket foundation. The weakening of the foundation-soil contact effect is the main reason for the degradation of mode frequency, and the corresponding explanation and discussion are made by the stiffness weakening effect of foundation-soil contact and the scouring effect.