Double-skin sheet reactor (DSSR) attracts attention in recent years due to the simple design and high mass transfer, but its application to photocatalytic CO2 reduction with immobilized catalyst is still a new trial. In this paper, the three-dimensional models describing the photocatalytic CO2 reduction in DSSR by means of solar energy were developed and numerically simulated, on the basis of the transient and continuous solar light distributions. A performance evaluation approach was proposed to guide the structural optimization of DSSR in photocatalytic CO2 reduction. The effects of operation parameters and reactor structures on CH3OH concentration were analyzed and discussed. The results show that the outlet CH3OH concentration of 2.68 x 10(-4) mol m(-3) in DSSR is much greater than that of 1.77 x 10(-5) mol m(-3) in optical fiber monolith reactor under the same conditions. It increases as both the inlet water vapor concentration ratio and day-average light flux increase, but decreases with increasing the inlet velocity, all of which are beneficial to the CH3OH productivity. The CH3OH concentration will decrease with the increase of the number of parallel-flow channels, but increase thanks to the rise in the width-height ratio and inserting flow guiding pieces, which are recommended for higher CH3OH concentration in the design of DSSR. (C) 2014 Elsevier Ltd. All rights reserved.