In order to reveal the variation characteristics of soil water and its availability of check dam area in the northern loess plateau,the paper took a check dam area which located at the Liudaogou basin of northern loess plateau,and based on the measured data of hydrology and meteorology to get the evapotranspiration (ET) of grassland and the reference crop evapotranspiration (ET0) by use of Penman equation and Penman Monteith equation,and evaluated water availability. Moisture availability was assessed based on the calculated results of ET and ET0. Based on the motion equation of unsaturated soil water (Richards formula),the paper developed a one-dimensional numerical model for soil water content and simulated the soil water content. The results indicated that: the coefficient of moisture availability is significantly influenced by topsoil water content and ET; the coefficient mean of moisture availability of the check dam area (0.31) is higher than that of the slope (0.17);the developed model exhibited relatively high simulation accuracy, both the correlation coefficient between observed soil water content and calculated result, and the Nash-Sutcliffe efficiency (NSE) are more than 0.90. The results can provide the basis and method reference for the further research on ET and soil water motion at the check dam area of northern loess plateau.