Abstract: Study on sedimentary facies and microfacies of the known reservoir of the Chang 6 member of the Yanchang formation in the Xiasiwan Oilfield indicates that the dominant reservoirs are distributary channels and river mouth bar microfacies in the delta frontal surfaces of this region. Also,the accumulation of oil and gas is controlled by gentle structures. And find that source bed,reservoir and cap rocks are in a excellent combination,providing conditions for large-scale hydrocarbon accumulations. The exploration should be planned around the identified pool and then extended to both east and west in direction.