With sulphoaluminate cement and fly ash as cementitious materials, the effects of foaming agent, water reducer and thickener on the thermal conductivity of foam concrete were studied by orthogonal experiment to determine the optimal combination. Five groups of foam concrete with different densities (300, 400, 500, 700, 900 kg / m3 ) were prepared, and the cross-sectional views of the samples were binarized by Photoshop image processing software. The pore structure characteristics such as porosity, roundness value and pore size distribution were analyzed by Image-Pro Plus ( IPP) software. The results show the primary and secondary order of the factors affecting the thermal conductivity of foam concrete is thickener content, foaming agent content, water reducer content. The density grade is negatively correlated with porosity and R2 is 0. 91. As the density increases, the pores proportion with roundness value of 1 also increases. The pore size distribution of foam concrete with different density grades follows the log-normal distribution approximately, the pore size mainly concentrates at 200 μm, and the proportion of large pore size gradually decreases with density increases.