As the core material of the vacuum insulation panel, micro structure and physical properties of porous materials have great influence on the thermal insulation performance. To study the thermal conductivity of porous material under vacuum condition, three typical porous materials, that is, granular, fibrous and foamy materials are involved in this paper, and a physical model based on the Lattice-Boltzmann method （LBM） is proposed. The key parameters of the model are obtained by scanning electron microscope image from real porous materials. Numerical simulation and analysis are made to study the influence of the vacuum degree and the equivalent diameter of the particles/fiber/cell hole versus thermal conductivity by D3Q15 model based on LBM. Comparison of simulation and experimental results explores the principles of the thermal conductivity variation versus physical properties and vacuum degree. The work is significant to optimize the structure of core materials and to improve the accuracy of effective thermal conductivity prediction.