With the help of the core, well logging, seismic data and so on, the fine investigation and analyses were conducted for Yaojia-Formation Member-1 in the western slope of Songliao Basin. The achievements showed that the climate of the multi-source composite shallow water delta depositional was dry, the ancient terrain was flat, the sources were pretty plenty and powerful, and moreover many drainage systems were well-developed, thus the following three subfacieses were divided: delta plain, delta front and front delta; the distributary channels of the former were characterized by the shallow waters, strong water power, small scale and fast flow; while the ones of the inner delta front were changed frequently and showed different degrees of sheet sand, and the distal bar and tip sheet sand in the outer delta front showed a large area of contiguous distribution; five sedimentary modes were well-developed: strong-source upper plain in the high-water-level region, low-source lower plain between the high and low water level areas, inner front mode in the nearshore low-water-level area, outer front in the middle bank's wave fluctuation belt and front delta in the offshore deep-water area.