Soil moisture plays a critical role in crop growth and vegetation restoration in the Loess Plateau.In order to analyze soil moisture's variation of the alfalfa plot and its impact on the soil water eco-environment,field experiments were conducted in 2002.At the same time, evapotranspiration of fallow land and some other crop fields were also studied as a contrast.The main results are as follows:(1)Precipitation in the rainy season plays an important role in the supplement of soil water in alfalfa plot.The soil moisture's dynamic period was identical with the rainy season,but the trend is getting dry.(2)Through a rainy season,the soil water content and soil moisture was declined in the alfalfa plot,but to the fallow land which were equal with the levels in April.(3)The same rainy season has different replenishment results on different crop fields.Alfalfa plot's evapotranspiration calculated in the top 3m soil layer was close to the millet and maize fields,higher than bean field,but lower than sorghum field.(4)The drying layer caused by long term's alfalfa's growing should be noticed.It's hard to recover the soil moisture in the dryed layer.