We present DG method for solving two-way coupling compressible gas-solid two-phase flow. Equations of both phases are discreted simultaneously, including convection term and source term. Splitting technique to discretize governing equations separately is avoided. Numerical flux of both phases is based on approximate Riemann solver. Dusty-gas shock tube problem with particles in low pressure section is simulated. Comparisons of equilibrium flow and frozen flow are made. Influence of particles in gas and interaction rules between two phases in relaxation zone behind shock are studied. It found that mass ratio of particles determines last equilibrium state and particles diameter determines transition process of two-phase flow from nonequilibrium to equilibrium flow. Namely, different diameter particles correspond to different relaxation time and distance. It shows that the numerical method proposed is reliable. It lays a foundation for more complicated gas-solid two-phase flow problems.