The Songliao Basin is a large-scale Mesozoic continental petroliferous basin. Based on analysis of high-resolution 3D seismic data, a large-scale lacustrine subaqueous channel system is identified in the lacustrine mudstone of the first member of the Nenjiang Formation in the central basin. This system is composed of 3 trunk channels and 4 tributary channels, and extended from north to south along the Daqing Placanticline with a maximum length of about 71 km and the largest width of about 600 m. This study indicates that this system may be resulted from river rushing into lake. Interpretation of logging and core indicates that there are rich petroliferous properties in these channel sand-bodies. Therefore, the discovery of this large-scale lacustrine subaqueous channel system will provide a new target for hydrocarbon reservoirs within the lacustrine mudstones in the central depression of the Songliao Basin.