A quantitative description of the evapotranspiration process taking place among the atmosphere,vegetation and soil is needed for studying air-land interaction and interrelation between the geosphere and the biosphere. In this paper, based on the theory of planetary boundary layer and soil-water dynamics, one dimensional soil-vegetation-atmosphere coupled numerical model is proposed. Parameterizations for upper soil layer and vegetation layer are developed.Through transfers and exchanges of heat and water, the thermal and moisture states of atmosphere, vegetation and soil are linked in a coupled system, in which vegetation is considered as a horizontally uniform layer, and the horizontal differences of soil variables in the system are neglected.It allows the surface to become moist quiukly during rainfall or to become drier than the bulk soil while evaporation occurs.An efficient one layer foliage parameterization is therefore developed that extends continuously from the cases of shielding factor σ^f=0 and shielding factor σ^f=0.5.It includs influences of both ground and foliage albedos and emissivities, net radiation, retained water on the foliage, and several other considerations.The evapotranspiration process and soil moisture content in the soil-vegetation-atmosphere system is simulated and the simulated and observed soil moisture contents are compared. The results show that the evapotranspiration can be divided into three stages with the variety of soil moisture near the surface. Soil property and vegetation shielding factor are the most important influence factors in this process.The preliminary results of the experiment indicate that the land surface process model is capable of predicting the thermal and evapotranspiration processes on the land surface and suitable for climate study.