The upper section of the First Group in Zhujiang Formation of Wenchang A/B/C Oil Field in Pearl River Mouth basin is developed in a neritic shelf sedimentary environment, whose main sand body of is a combination of offshore shallow and offshore bar, the latter microfacies manifests as relatively high-quality reservoir which owes to the potamic transport, highly sand-cleaning effect, relatively low mud contend and relatively pure sandstone. However, the current situation that offshore bar microfacies changes rapidly in the plane and in vertical, making the superimposed relationship among sand body unsharp accordingly. It is necessary and significant to analyze the sedimentary feature of offshore shallow and offshore bar microfacies, as well as confirm the rule of sandstones distribution to predict advantageous reservoir.By analyzing the sedimentary differences among three oil fields, the results indicate that the distributed direction of sand body is controlled by structural trend, the porosity and permeability of sand body is up to the distance towards provenance region and the depth of water. Wenchang B Oil Field, which is close to the provenance region and belongs to shallow-water area, has an advantageous reservoir distribution with its offshore bar located in the higher position of structure; Wenchang A Oil Field, which is far from the provenance region and belongs to deep-water area, has the worst physical properties; Wenchang C Oil Field has medium physical properties.