An accurate estimation of building material thermal conductivity is crucial for the modeling of heat transfer processes and the calculation of building energy consumption. The effect of moisture content on the thermal conductivity of the material is usually neglected in most currently used calculation methods. These methods cannot represent the interior multi-phase heat transfer process. In this paper, the coexisting solid-liquid-gas thermal conductivity physical model was proposed. Taking into account the pore structure characteristics of building materials, a coexisting tri-phase thermal conductivity calculation model based on capillary structure was established using fractal theory. The quantitative influence relationship of the parameters, such as porosity, pore diameter distribution, moisture content and fractal structure, on the thermal conductivity of moist porous materials was analyzed. The results provide a theoretical basis for the thermal conductivity correction of moist building materials. (C) 2018 Elsevier Ltd. All rights reserved.