This paper analyzes the dynamic characteristics of the variations of the beach volumes for three level zones of the Yanjing Beach in the Shuidong Bay of the western Guangdong Province by using the methods of dynamic system analysis and the multi-dimensional spectral estimation. The results show that the variations of the beach volume are characterized by the multiband oscillations with a dominant semimonth period. Upwards the low tide level, the beach tends to be stable. The estimates of the partial coherenees and the partial phases indicate that the variations of the beach volumes are mainly the results of the direct actions of the waves which are influenced by the tidal level changes and driven by the wind stress. The simulation results of the beach volume series for different beach height zones by threshold mixed regressive models indicate that the influence of the tide on the variations of the beach volumes is weak-ened and the direct actions of the wave energy and the wind stress are apparently enhanced with the increase of the beach height.