Based on the background of the Donghai Bridge offshore wind farm project, a series of long-term undrained cyclic loading triaxial tests were carried out on the reconstructed saturated silty clay through the dynamic triaxial system. Considering the confining pressure, dynamic stress ratio and frequency, the dynamic weakening characteristics of powder clay under high frequency (f>5 Hz) were studied. The results show that the cumulative plastic strain and cumulative pore pressure increase with the increase of thecycles and tend to be stable, which shows the strain softening and the pore pressure softening. The secant dynamic deformation modulus and the secant dynamic elastic stiffness modulus first decrease sharply with the increase of the cycles, and then become stabilized, which shows the weakening of stiffness. We further discusses the relationship between the secant dynamic elastic stiffness modulus and cyclic strain amplitude, and the dynamic stress ratio and the frequency has little influence on the attenuation trend of secant dynamic elastic stiffness modulus, but the confining pressure has great influence. The higher the confining pressure is, the more slowly the secant dynamic elastic stiffness modulus decay and the lower attenuation stable amplitude is.