Abstract: Based on core observation and in combination with a-nalysis of grain sizes, microscopic section, digital processing results of well logging data, the 5 cored wells in the northern part of the west block in Gudao oilfield are analyzed in respects of lithology, architecture and sedimentary structure, and the sedimentary microfacies of the sand units 3 - 6 in the upper Guantao Fm are studied. It is believed that the interval of interest in this area is of meandering river deposits. The fluvial facies is divided into riverbed, bank, overbank and abandoned channel subfacies, which are further divided into riverbed lag deposits, point bar, natural levee, crevasse-splay and flood plain microfacies.