Abstract: The 3rd member of Paleoproterozoic Dashiqiao formation in Pianling, Xiuyan County, Eastern Liaoning can be subdivided into 6 lithologic layers, each of which has different characters of lithologic assemblage. The CaO/MgO ratio of carbonate rock is an indicator for sedimentary environment. With analysis on the characters of lithologic assemblage and the CaO/MgO ratio of each layer, it is inferred that the sedimentary environment of Late Dashiqiao age in Pianling area was evolved in the process of arid lagoon and closed bay-open shallow sea-shore-arid lagoon and close bay-shallow sea (occasionally intertidal zone or shore)-alternative of shore and shallow sea.