Due to the complex microstructure in aerogels and the intricate heat transfer mechanism of solid-gas coupling heat conduction, modeling of the gas-contributed thermal conductivity of this type of material is quite difficult. The present work introduces a novel numerical methodology for computing the gas contributed thermal conductivity of aerogels by analyzing their microstructural characteristics and heat transfer mechanism of the thermal coupling between the gas phase and the solid backbone of the system. Specifically, structures of aerogels are reconstructed by an improved three-dimensional diffusion-limited cluster-cluster aggregation (DLCA) method, and the contribution of the solid-gas coupling heat transfer to the gas-contributed thermal conductivity of aerogels is quantified. The present numerical model is fully validated by the available experimental data for different aerogels with porosity ranging from 78% to 97.7%. The proposed numerical method is flexible and versatile because it is capable to account for both the geometrical and topological details of the aerogel structure. (C) 2018 Elsevier Ltd. All rights reserved.