Based on the theory of sedimentology and sequence stratigraphy, and by analysis of seismic response characteristics, well logs, core sedimentary structures, the regional geological conditions and distribution of heavy minerals, it is concluded that two complete sublacustrine fans developed in the third Member of Shahejie Formation of Gangzhong Oilfield, which cover 30 km² to 50 km² and each exhibit a positive cyclic sedimentary sequence. There are two regional erosional interfaces for stratigraphic reservoirs at the ends of middle and upper oil groups, the third Member of Shahejie Formation. The sublacustrine fans with quite large area and braided channel developed on it, where the sandstone pinches out in the mudstone, is easy to form lens and wedge outs of sandstone lithologic reservoirs.