Pores and fractures in rocks described with the aspect ratio as their shapes can be simulated by ellipsoids. The Berryman dispersion method was used in this paper, with which the Poisson's ratio, velocity and density of porous rocks are related to the porosity, fluid saturation and pore aspect ratio. The effect of aspect ratio on AVO response was also studied by a shale/sand modeling. The results show that the reflectivity or amplitude versus incidence varies with the aspect ratio change under the condition of the same mineral component and porosity, and the distinguishability of gas in AVO cross-plot decreases with the increasing aspect ratio. The smaller the aspect ratio, the easier the gas layer recognition by cross-plot.