The thermal conductivity of glass fiber and ceramic fiber is the lowest compared with foam and powder core materials when internal pressure of the material is less than 100 Pa. In order to study the impact factors of thermal properties of fiber, the internal structure of fiber is constructed based on the principle of random parameter,and effects of fiber diameter,fiber length and porosity on thermal conductivity are analyzed by combining with Lattice-Boltzmann method (LBM). Moreover, the simulation results are compared with experimental results,and results show that simulation and experiment have a good agreement with each other,which indicates that the method used in this paper can predict the thermal conductivity of fiber effectively.