The debris flow sediment is located at Laomao mountain gullies, in south Liaoning province, which forms in unique physical geog raphical environment of east coastland of China. The area belongs to temperate zone,monsoon climate is regulated by intense martin climate. Precipitation concent rates in summer by the type of torrential rain. This condition helps to debris flow process. In view of mechanism, the debris flow is unique rapid and temporary torrential rain-typed one. Sedimentary structures of the debris flow show bulky grain size migmatite. By analyzing the sediment grain sizes, the author leads into concept of likelihood of grain size distribution and pursues the debris flow grain size distribution patterns.