In catchment basins whose depth of water is deep enough, hyperpycnal flows develop when the flow carries sediment particles in large quantity, making the fluid density being greater than the water density in stable environment, being a kind of high density fluid flow along the bottom of the basin without much effect from the buoyancy. The threshold density of sediment to develop hyperpycnal flows in marine environment is 36~43kg/m3, and 1.3%~1.7% of volume concentration. Hyperpycnal flows would mainly be triggered by flood, and formed from the estuary into catchment basins through different regions of backwater zone, depth limited plume zone and plunging plume zone. Hyperpycnal flows are produced through three major sedimentation stages as early deposition, erosion—bypass and late deposition, making the sedimentation erosion—filling proximal whereas continuous deposition distal. The formation and sedimentation of hyperpycnal flows are controlled by factors of topography, climate and source, and hyperpycnal flows are likely to develop under conditions of obvious terrain elevation difference, semiarid climate conditions and abundant fine suspended sediments supply. The sedimentary characteristics and sedimentary structure are controlled by the “source to sink” system, and are distinct from other deep water gravity flow deposits because of the typical sedimentary structures such as water causes cross beddings, the sharp contact surfaces between layers or erosion contact surfaces and coal fragments and leaves. As for sedimentary structure of hyperpycnites, massive sand bed, inversely to normally graded bed, thin layer and fine grained bed develop in turn from proximal to distal. The research of hyperpycnal flows is of great significance, which would enrich and perfect the deep water gravity flow theory, explore the paleoclimate change and paloeflood regularity, explain sedimentary characteristics of the deep water gravity flow and sand body distribution and direct deep water conventional and unconventional petroleum exploration as well.