Abstract: Dynamic data analysis and harmonic wave theory are applied to simulate and ana-lyze perildic changes in soil moisture under different modes of artificial disturbnce in Chinese fir plantation．Results showed that soil moisture series on the forest land is sup-perposed by a stochastic component，which is a reflection of the effect of stochastic flue-tuations of climate on soil water content，and a perildic deterministic process，which is a reflection of periodic changes in climate or combinations of the water requirements of trees and periodic variations of climate．Simulation of the soil moisture series of clearcut-ting，control and thinning watersheds demonstrates that the additive model is of high precision for modelling long term change process of soil water．Periodic vibration de- creases in the order of：thinning>control>clearcutting，and the vibration of the three watersheds abates significantly with the increasing of soil depth．

Key words: Chinese fir, Disturbance, Soil water content, Harmonic wave, Simula-tion