It is a complex area in the southern part of Orxon Depression, Hailar Basin, because of complicated faults and structures, multisource, short sediment source and fast facies change of Lower Cretaceous Nantun Formation, all of which lead to difficult prediction to the favorable target area. Aiming to the problem, and guided by the sequence stratigraphy and "slope break" theory, a serial of innovative techniques including the 3-D seismic fine interpretation, the sandstone description and the 3-D visualization interpretation for complicated target areas is established for this study. By using these new techniques, three slope break belts are found in Eastern Orxon Slope. It is regarded that the downdip part of the third slope break belt and the second slope break belt are favourable to form lithologic hydrocarbon reservoirs. 10 good Nantun Formation fan bodies with a total area of 145km2 are distinguished out in the third slop and 5 wells were drilled, in which 4 wells of commercial oil flow and 1 well of low-yielded oil flow are obtained. The rate of well coincidence is 100,.