Abstract: The sandbodies in the 3rd Member of Shahejie Formation in Western Sag with a huge sedimentary thickness and a wide distribution are the most important reservoirs for petroleum accumulation in the deeply buried sequences in Liaohe basin. Based on core, drilling, logging and seismic data, seven types of sedimentary facies are identified in this area, i.e., alluvial fan, fan delta, beachy turbidite fan, off-shore turbidite fan, fault trough gravity flow channel, slump turbidite fan and lacustrine facies, in which the multistory sandbodies in the fan delta and turbidite fan comprise the best reservoirs in the area. Five sets of depositional system are mainly developed during the sedimentation of the 3rd Member of Shahejie Formation, with the alluvial fan-fan deltasublacustrine fan depositional system dominant; At the early-middle period of the 3rd Member of Shahejie Formation, the lake basin showed transgression depositional sequence. The sandbodies of fan delta and off-shore turbidite fan in western slope area gradually moved eastward and the distribution range expanded little by little, while in eastern steep slope area, the facies belts of each subfacies of fan delta narrowed down gradually and the sandbodies of beachy turbidite fan were distributed in belts; At the late period of the 3rd Member of Shahejie Formation, the lake basin showed dereliction depositional sequence. The distribution range and thickness of sandbodies in the western slope area succeeded the characteristics of the earlier period on the whole,however, the facies belts of each subfacies of fan delta in eastern steep slope area widened gradually and went forward to the center of depressed area of the lake basin; The features of distribution and migration of sedimentary facies belts indicate that the sedimentary framework was controlled by several factors, including palaeotopography, boundary growth fault, relative change of lake surface and provenance efficiency.