Due to the utilization of concentrated solar energy, a more complex high-temperature thermal environment will be formed inside the solar thermochemical reactor, thereby resulting in complicated behaviors of chemical reactions. This paper numerically investigates the carbon deposition behaviors inside a Ni/Al2O3-based catalyst porous-filled solar thermochemical reactor for the dry reforming of methane (DRM) process under various operational conditions. The reaction kinetics for DRM including four side reactions are programmed via UDFs. The simulation results indicate that the optimal structural parameters of porous media for high-value syngas products with less carbon deposition are phi = 0.8 and d(p) = 2 mm, while the optimal feed ratio is CH4/CO2 = 1. Besides, the operating condition at nu(in) = 100 mL/min and P-lamp = 0.7 kW has the advantage of obtaining higher conversion rate while reducing the carbon deposition rate to some extent.