Abstract: The Songkaersu formation of Lower Carboniferous is distributed in the south and north sides of anticlinorium in south piedmont of Kelameili mountain. To understand the lithological feature of it and contact relationship with above and beneath horizons can provide fundamental data for petroleum exploration in this area. The study shows that the eastern Shuangjingzi area occurs continental coarse clastic rock and unconformable contact with underlying Tamugang formation; the western Shuangjingzi area (i.e. east Laoyinggou?Wucaiwan area) appears large volcanic formation interbedded with sedimentary rock. The west’s Songkaersu formation can be divided into lower sub?formation (C1s a, dominated by volcanic rock) and upper one (C1s b by sedimentary rock), they are in conformable contact. The Batamayineishan strata in original Wucaiwan area and Jianshangou-Shaqiuhe area should belong to the lower sub?formation of Songkaersu formation