At present, the environment reconst ruction project in the loess plateau area needs the support of the accurate slope gradient. The slope data are mainly detained from the digital elevation model. Four different test areas are chosen to learn the estimation way of the slope gradient from DEM and set up a slope accuracy simulation math-model by assuming 1∶10000 scale, 5mreso lution DEM as the basis, and applying relation analysis, regression analysis. This model was testified to be available in application, which also present the important way to set up the general model of the national scale