Abstract: On the base of engineering geologic investigation to Storage side slope of three-gorges reservoir area, the con-cept of earth-rock mixed construction is advanced fornally, and according to it, we made unified engineering classification for natural geologic body, partitioning the geologic body for rock mass, earth-nxk mixed construction, earth mass. It is detail to earth-nxk mixed construction method of classification, determination of indicatrix, advantage and comparison with other methods. At last two are given.