The precipitation on dry slopeland of loess plateau region is approximately distributed as follows: the ground runoff makes up less than 5%～10%,the ground evaporation accounts for about 45%～ 50%；and the plant transpiration amounts to 45%～50%.So the work of soil and water conserv ation on dry slopeland should not only consider the infil tration and retaining of ground runoff,the reducing of evaporation from the earth 's surface should be more valued.The eco-ag riculture system on dry slopel and of“ ground covering+ bio bar rier”could reduce the ground evaporation effectively, and control soil erosion and raise the crop yield by a big margin. It calls for small investments and yield quick returns, and it is sui table for larg-scale spreading.