Abstract: According to the divide of rocks stratigraphic units stipulated in ‘China stratigraphy guide' (2001) and the continuous sedimentary clastic rocks widespread outcrop in Yilehuli mountain area, the five Formations of Niqiuhe Formation (S₃-D₂n), Genlihe Formation (D_2-3g), Xiaohelihe Formation (D₃x), Huadaqi Formation (C₁h) and Chargelahe Formation (C₁c) would be consolidated as a group named Liaoyuan Group (S₃-C₁L).Take Chargelahe area in Heihe city as a typical example, Liaoyuan Group (S₃-C₁L) has been divided into the Upper and Lower Liaoyuan Group respectively.The Lower Liaoyuan Group (S₃-C₁L^a) includes Niqiuhe Formation and Genlihe Formation, while the other Xiaohelihe Formation, Huadaqi Formation and Chargelahe Formation belong to the Upper Liaoyuan Group (S₃-C₁L^b).In the process of regulating the lithostratigraphic units, based on the analysis of lateral comparison and division of stratigraphic sequences, it is considered that the Lower Liaoyuan Group consists of marine clastic rocks while the composition of the Upper Liaoyuan Group is continental clastic rocks.The relationship among each Formation in the Liaoyuan Group is conformity.The lower boundary of the Liaoyuan Group is limited on the disappearance of sandstone containing gravel in underlayer Woduhe Formation (S₃w), While the upper boundary of which is not integrity.According to fossil record, the period of the Liaoyuan Group is from the Late Silurian to Early Carboniferous.