The effective absorption of photons by photocatalyst in the reactor is a challenge for scaled-up application of a photocatalytic hydrogen production system. The spatial distribution of radiation and photon absorption are proposed to be strongly dependent on the photocatalyst concentration and the structure of the solar collector. However, there have been few reports of the radiation absorption properties of a cylindrical reactor based on high power solar collector that is suitable for a large-scale photocatalytic hydrogen production system. In this study, the distribution of radiation in the reactor as represented by the local volumetric rate of photon absorption was determined by adopting the modified six-flux absorption scattering model based on the compound parabolic concentrator and the surface uniform concentrator. The explanations of the differences of radiation absorption properties were comprehensively analyzed by ray-tracking technique. The structure of the solar collector and the optimum catalyst concentration are recommended based on photon absorption efficiency. This work may serve as potential reference values for the optimal reactor operating parameters for large-scale application.