Abstract: In accordance with core and thin section observation,the oosparite and algal bindstone of S69-S76 wells on the southern margin of Tahe oilfield is in contrast with the micrite,sparry limerudite or limearenite and microspar limearenite in the other areas.So,the boundary of the Early Ordovician sedimentary framework should be shifted westward to the line along Kunan 2 to Mancan 1 wells.According to lithology,rock texture,sedimentary tectonics,section structire,paleontological assemblages and other marks,open platform,intraplatform shoal and platform-marginal knob-and-beach three types of sedimentary facies were recognized in the Lower Ordovician,and deeper-water shelf and peritidal sedimentary facies were recognized in the Middle-Upper Ordovician.From the angle of sequence stratigraphy,the Lower Ordovician can be divided into transgressive and high-water level system domains two secondary sequences,and the Middle-Upper Ordovician can be divided into transgressive,high-water level and low-water level system domains.Meantime,the development characteristics of sequences and system domains were studied,and the comparison scheme of the Lower Ordovician sequence stratigraphy was determined preliminarily.