Abstract: Chenjia depression is the main oil source area in the west sag of Liaohe basin. Several series of turbidite sandbodies and huge thick mudstone are developed in its lower Sha3 sub-member. The depression has the condition of forming formation lithologic trap. Using the seismic attribute analysis, frequency division and model-based impedance inversion, the sedimentary laws and distribution characteristics of sandbody in lower Sha3 sub-member was described and analyzed, and the favorable area of sand distribution was forecasted. Based on the results，combined with the drilling, logging and core data, the beneficial sandbody of the top of 4thSQ2 and 4thSQ3 was identified. Referred with the division results of sedimentary faceis, the forming pattern of formation lithologic trap in lower Sha3 sub-member was analyzed, and the distribution of beneficial traps was predicted.