A set of Early Jurassic fresh water Bivalvia assemblage, Qiyangia assemblage, was discovered recently from the "Qoima Co Formation" in Duxue Mountain area, Qiangtang basin, north Xizang (Tibet). The "Qoima Co Formation" overlies unconformably ly on the the Early Jurassic volcanics, was considered Middle Jurassic before, is composed of a set of marine-continental interbedded sediments, from coarse debric rocks, limestone to fine debric rocks, is continuous with overlying Middle Jurassic. Based on these new data, the lithostratigraphic division program of this Early Jurassic sediments was discussed. It is pointed out that considering the Jurassic lithostratigraphic units in the Yanshiping area as contemporary units in northwestern Qiangtang basin is inappropriate. It is necessary to recognize the stratigraphic frame in northern Qiangtang basin.