Based on the equation group of reflection coefficient and transmission coefficient in the interface of two types of dual-phases mediums, three equation groups of reflection coefficient and transmission coefficient in three kinds of interfaces have been derived, which are the interface between one-phase and dual-phase medium that is the top of reservoir, dual-phase and one-phase that is the bottom of reservoir, one-phase and one-phase medium that is the interface of two tight rocks. The AVO equation group from one-phase to dual-phase has been produced comprehensively. The relationship formula have been built between parameters（A, N, Q, R, ρ₁₁, ρ₁₂, ρ₂₂, Ø） of the dual-phase medium and prime wave velocity, second wave velocity, density, porous and kind of fluid that include brine, oil and gas. All of these studies have made a beneficial exploration of AVO theory in dual-phase medium to practice. Three kinds of lithological interfaces have been designed. The reflection coefficient curves of different interfaces have been calculated respectively by dual-phase medium AVO equation and Zeoppritz equation, which provedhat Zeoppritz equation is a special case of dual-phase medium AVO equation.