Abstract: The Pingliang Formation in Qishan area is composed of dark mudstone, siltstone and argillaceous limestone with imbedded thin layered bentonites. There are obvious differences between the Pingliang Formation and its overlying as well as underlying strata on rock type, sedimentary environment and tectonic background. The research on sedimentary characteristics, tectonic background and formation environment has theoretical significance for revealing Late Ordovician paleogeography, paleoclimate and paleotectonics in the Ordos Basin. Based on profile measurement and microscopic identification, the stratigraphy, petrology and sedimentary facies of the Pingliang Formation have been studied in detail. All of these results indicate that the Pingliang Formation can be divided into three sedimentary cycles according to the petrological features. The first sedimentary cycle mainly consists of mudstone and sandstone with relatively small quantity of limestone. The sedimentary facies are mainly composed of turbidite deposition, arenarious contour current and argillaceous contour current deposits. In the second sedimentary cycle, the proportion between mudstone and limestone is similar. The sedimentary facies are mainly composed of argillaceous contour current deposits and cinereal contour current deposits. The third cycle comprises mainly sandstone and mudstone with small amount of limestone. The sedimentary facies are mainly composed of arenarious contour current with a small amount of cinereal contour current deposits.