In order to evaluate the influence of water consumption by the planted trees on the fluctuation of groundwater level in Mu Us desert in Inner Mongolia, China, a numerical simulation model was developed. The model consists of two parts: 1) Dry Sand Layer Model (DSLM); 2) Groundwater Level simulation Model (GLM) with the sub model which represents the absorbing distribution of the trees. Inputting some meteorological data, the timesequential changes of the soil moisture, the roots absorbing characteristics and the groundwater level could be simulated by GLM using the infiltration rate below the dry sand layer calculated by DSLM. Using three factors observed and surveyed that were the meteorological data, the soil moisture properties and the transpiration characteristics of planted trees, we tried to reproduce the fluctuation of groundwater level observed at the non-tree condition and to simulate the changes of ground water level at the semi-fixed dune. According to the former calculation result, this model could reproduce the observed ground water level by relevant evaluations of the soil moisture properties, the infiltration rate and the sink intensity from the groundwater zone. The simulated results suggest that even without direct absorption form the ground water body, the trees planted excessively high density would decline the groundwater level from year to year through the water consumption from unsaturated zone.

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