Abstract: Shaximiao gas reservoir in Xinchang district is river delta sand with a relatively big thickness and high porosity, and the mapping feature of the reservoir is clear. Exploration and development of the reservoir demonstrate that the gas area of the reservoir is constrained both by the sand body itself and the structure characters, and the gas-water contact is very complex. With the acquisition of 3D3C seismic data and in order to overcome the uncertainty of the prior model of “low frequency and strong amplitude”, we synthesized shear wave log, forward inversed the AVO gather, analyzed and compared differences of the AVO characters of gas sand and water sand, and carried out AVO inversion. The potential gas and water distribution area has been detected by crossploting impedance and Paoisson’s ratio. Based on the prediction, wells have been successfully planed, indicating that prestack AVO inversion does have great advantages over conventional interpretation of seismic attributes.