A kind of sediment --Oncolitic limestone was discovered in first and second sandstone set of Gaotaizi oil layer in the second and third sections of Qingshankou Formation of Early Cretaceous in the boundary of Longhupao-Daan rank ground and Taikang uplift zone of middle depression in Songliao Basin, the most typical oncolite occur in the second and third sections of the Qingshankou Formation of du30 wells. The thickness of the oncolite limestone layer is roughly 40cm, the depth is 1415.36-1415.77m. Oncolite color with gray and brown,the shape of oncolite is globosity、ellipsoid、oblatus and tuberose. By the research we think that the type of formation environment of oncolite in this area has primarily two:one is the underground shallow bay facies of lake delta front,the other is sand and dam facies of the brink and shallow lake. The lake basin atrophies in the period of Qingshankou Formation, along with take face lake migration in the basin, the oncolite growth layer also headings up the migration, expressing the good environment instructions meaning.The condition of less of land sources supply、the water environment of the deep of water、warm weather and motion water is good to the form of the insect and the material precipitates and growth of the rolling oncolite,so oncolite is a large quantity layer growth in Xiaolinke-Qijia region of Songliao Basin.