Through the outdoors exploration and laboratory analysis, it in detail studies the feature of Paleozoic strata in Xi Ujimqin applying stratigraphic theory and method, and then builds the lithostratigraphic framework, biostratigraphic framework, chrono- stratigraphic framework and sequence stratigraphic framework. It finds that the structural unit, where the studied area is, is a rift basin between Siberia plate and North China plate, whose joint time is late Paleozoic Devonian, and rebuilds the lithofacies ...