Located in middle Biyang sag, the Bidian area is a deep-waterdeposition area with sand_bearing ratios being mostly 20%. There exist typical sedimentary gravity flows in the Bidian area, and two kinds of facies, i.e.,lacustrine facies and sublacustrine fan facies, were identified in Ⅲ～Ⅳ sand-bed sets of 3rd Member of Hetaoyuan Formation. Sliding evidence of fluidized flows, slips, pull-apart and drop-down rock masses could be found from well cores. In addition,ripple cross laminations, water_escaping structure and dish_shaped structure also grew, with the last two phenomena developed in the Bouma sequence of C segment, in association with the ripple cross laminations. Flat and conformable beds formed by turbidites of Bouma BE segments are seen above and below the rock masses. The layer-flattening seismic profiles also show that, before the deposition of the second sand_bed set of 3rd Member of Hetaoyuan Formation, there existed parallel and sub_parallel seismic reflections interbedded with lentoid or wavy, eyeball_shaped textures. It is held that the parallel and sub_parallel textures probably represent background sediments of deep-water mudstones, whereas the wavy and eyeball_shaped textures represent typical sublacustrine fans.