Abstract: We took Shenmu,Suide,Yanchuan,Fu County and Yijun as the five major sample areas,which have different landforms in the Loess Plateau,according to the map scale at 1∶10 000 as the DEMs objectly.For each sample area,the variation rules of the information amount of the slope and aspect derived by DEMs with differently horizontal resolutions were analyzed and the index of the mutual information was proposed.The relationship between the index and different horizontal resolutions is obtained in 20 experimental areas.If the index is known,the required horizontal resolution can be calculated according to its inverse function.The relationship model has passed test in 16 randomly selected test areas.The experimental results show that the model can decrease the amount of data and cut down the costs whilst keeping the accuracy.