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The southwest region of Qaidam, in the sedimentary period in Paleogene, with relatively flat structure and basal stability evenly subsidence, was formed the "broad and shallow lake basin" ancient terrain. Ancient climate is arid or semi-arid environment, and such climate caused the intense physical weathering in source rock. The ancient water is shallow, less than 10m, and lake level fluctuation is frequent, with lake level cycle variation. Terrigenous detrital material in flat structure basin was carried for a long distance by large rivers, which provided forming conditions for a large shallow water delta. The southwest region in Paleogene mainly exists in the five source supply directions, such as the provenance of the Altyn mountain, Tiemulike, Qimantag Mountains, east Chai mountain. According to the relationship of lake basin climate changing and the lake level changes, the form of the shallow water delta sand body can be classified into three types, sheet, lump and branch shape.