In this work, the reflection coefficient formula of spherical reflected P wave was derived. According to the derived formula, the variations of reflection coefficient and phases of class I and class III AVO media versus angle were calculated, and compared with the result of plane wave Zoeppritz formula. The results show that for the class I AVO medium, spherical wave reflection coefficient near the critical angle is more accurate than the Zoeppritz's computation result, and is highly influenced by the interface depth, i.e. with depth increasing, the trend of spherical wave AVO is close to plane wave AVO. Finally, numerical simulation technology was applied to verify and analyze the spherical wave AVO gather. The results show that a larger variation occurs for the refraction caused by the near-critical or super-critical angle through the class I AVO medium. But for the class III AVO phenomenon, because there is no critical angle problem, the spherical wave simulation results has little difference with Zoeppritz's. These calculation and analysis results would provide a theoretical basis for the AVO analysis of large offset gather data in practice.
