The volumetric solar receiver is an important component of Concentrated Solar Power (CSP) system. In recent years, some studies concerned with the novel structures of the volumetric solar receiver have been conducted. In this paper, a gradually-varied volumetric solar receiver is proposed. The major feature of this structure is its porosity which decreases gradually from the front surface to the rear surface. Based on the modified random spherical bubbles method, a 3D computational model of this porosity changed solar receiver is reconstructed. In addition, by combining with the Monte Carlo Ray Tracing (MCRT) method, the optical and radiative properties of this receiver are investigated. The results show that the reflection loss could be reduced owing to the lower reflectivity of this structure. It also outperforms in solar energy absorption compared with the uniform structures that are examined in this paper and exhibits a uniform solar radiative flux distribution inside the receiver. Finally, with the use of genetic algorithm, the porosity distribution of the gradually-varied volumetric solar receiver is further optimized, which leads to a much larger penetration depth of solar radiation. These results suggest that the gradually-varied porous structure provides a novel design method to enhance the solar radiation absorption and the volumetric absorption of a volumetric solar receiver. (C) 2017 Elsevier Ltd. All rights reserved.