Solar driven CO2 reforming of methane has attracted increasing interest, due to the greenhouse effect and the depletion of fossil fuel energy. The design of foam structure parameters in volumetric solar reactor significantly affects the transport phenomena and overall reforming performance. A numerical model is developed in this study, coupling the conduction, convection and radiative heat transfer with the chemical reaction kinetics. The radiative transfer in foam structure is solved by the modified P1 approximation, and local thermal non-equilibrium model is used to account for the temperature difference between the fluid and solid phases. The reforming process in solar reactors with gradual foam structure parameter (porosity and cell size) both in axial and radial directions is analyzed. Thermal and reforming performances in different configurations are compared in detail. The results indicate that the methane conversion almost increases gradually with the increasing of porosity and cell size for the reactor with uniform foam structure. The decreasing designs of structure parameter either in axial or radial direction have better performance than the increasing ones. Besides, the increasing and decreasing designs in radial direction have a noticeable difference in the mole fraction distribution of reactants and products from those in axial directions. (C) 2018 Elsevier Ltd. All rights reserved.