Abstract: Delta lies in the intermediate zone between the sea and land or lake and land,and it is also a very important part of them. Because the slope of lake bottom is low, it is the channel which plays a leading role to the formation of rather long sub-sea distributary chinnel. Chang 3₃ reservoir of Bai 120 tract is a typical example. Bai 120 tract has intact sedimentary unit. There is a channel deposit zone in the middle of Bai120 tract, two natural barriers which are higher than channel outside, and there are four sand lobes in the end;a small creva sse channel being in the middle of that. The sand bodies distribute like a bar-finger, symmertrizing on the right and left sides,having typical biconvex of a delta sub-sea distributary. chinnel. The channel deposit cross flow in the west,three lobes in the end and parts of natural barries in the west are the good reservoirs because of better physical properties. Natural barriers in the east,parts of the west and cross flow zones are dry because of the poor physical properities. Among these rservoirs,natural barriers in the east are the seal to the up-dip direction of south and north. The author builds up a perfect model of sub-sea distributary chinnel deposit,which willen rich deposit theory on delta.