Abstract: Abstract：Massive and almost unmetamorphosed marine sedimentary strata mainly composed of volcanic rocks, clastic rocks, carbonate rocks are exposed on the northern slope of the Altun Mountains. Based on measuring the lateral section in this area, the authors have found that the strata unconformably overlie mesometamorphic Changchengian strata. Fossils such as radiolarian and sponge spicule are present in siliceous rocks of the study area, and studies show that these fossils belong to middle-late Ordovician period. According to these findings, the authors have re-determined and subdivided the strata.