Abstract: Guantao formation in Huanghekou sag is dominated by braided-river deposits and is lack of mudstone cap rocks, enough attention has not been paid to the exploration in the formation. Based on the comprehensive analysis on the data of core, logging and seismic, it is considered that the braided-river deposits and meandering river deposits are developed in the southern slope belt of Huanghekou sag. Using the sequence stratigraphy analysis method, the paper establishes a sequence stratigraphic framework for the Guantao formation in the study area, and classifies two 3-order sequences, namely SQG2 and SQG1, each of which contains a high accommodation system tract (HAST) and a low accommodation system tract (LAST). Based on which, the paper summarizes the characteristics of the sedimentary sequence evolution of Guantao formation in the study area. The study area was dominated by braided river deposits which mainly contained multi-period composite braided river sandbodies during the development of the low accommodation system tract of SQG2; during the development of the high accommodation system tract of SQG2, the study area was dominated by meandering river deposits which mainly contained isolated point-bar sandbodies and a high proportion of flood plain mud. The evolution characteristics of SQG1 sequence was similar to that of the lower Guantao formation. During the development of SQG1 sequence, the accommodation maintained a high level, so the grain size and sandstone percentage of the sandbodies in SQG1 were lower than those of Guantao formation. The 2 sets of meandering river deposits in Guantao formation of the southern gentle slope belt in Huanghekou sag can be the good cap rocks and provide good conditions for oil and gas accumulation. Guided by the study, oil and gas have been discovered successively in the study area