Based on seismic,logging and core data,the 4^th-order sequence stratigraphic framework of the Member 2 and lower Member 3 of Upper Cretaceous Qingshankou Formation in the west slope of the Songliao Basin was established and the spatial distribution of the sedimentary microfacies under the framework of the 4^th-order sequence was reconstructed. The Qingshankou Formation was divided into two 4^th-order sequences(Cg4、Cg3),each of the 4^th-order sequence was divided into lake expanding system tract and lake shrinking system tract,respectively named Eg4、Sg4,Eg3、Sg3 upwardly. Shore-shallow lacustrine sedimentary bodies(shore-shallow lacustrine sandy bars,mud bank and mixed bank)and delta front(mouth bars and distal bars) characterised the deposition pattern of the Member 2 and lower Member 3 of Qingshankou Formation in west slope. Delta front sedimentary bodies from the west and north were developed in the Eg4, shore-shallow lacustrine mixed beaches were developed among the sedimentary bodies of delta front. The early delta expanded and a new northwest delta was developed in Sg4. Delta from the west and north extended to the east and delta front sedimentary bodies from the southwest shrinked in Eg3. Delta front sedimentary bodies were dominant and overlapped each other, while shore-shallow lacustrine sediments reduced in Sg3. The depositional zones continued to expand,and delta front sedimentary bodies expanded in the Member 2 and lower Member 3 of Qingshankou Formation upwardly.