Gas-solid riser flow exhibits strong heterogeneous structure in both axial direction and radial directions. Recent experimental studies reveal that the general radial solids concentration profiles present a double ring structure and the formation of a solid core region which have a relative higher concentration than the annulus region. This paper is focused on a comprehensive modeling of continuous gas-solids flow structure both in radial and axial directions. The specific transport mechanism due to collisional diffusive mass transfer and turbulent mass transfer are modeled. The radial heterogeneous flow structure of solids and gas at the different stage of the riser are investigated in detail. This mechanistic model, implemented with a detailed axial flow structure model, consists of a set of coupled ordinary-differential equations developed from conservation laws of mass, momentum and kinetic energy of both gas and solids phases. The solving algorithm is based on the Runge-Kutta method. The proposed model predicts the phase transport profiles such as the solids concentration, phase velocities and pressure drops in different regions along the riser. The model also yields the critical information of flow structure characteristics such as back flow, wall frictions and choking.