Abstract: The thermal conductivity of graphite, carbon fiber modified thermoplastic polyimide was measured, and the effects of the filler content on the mechanical properties and thermal conductivity were investigated. The beha-viors of the thermal conduction of TPI composites were simulated by the Nielsen model and finite element method (FEM), and the shape of the filler was also considered. The results indicate that thermal conductivity of the material is improved obviously by increasing the filler content. The difference between the calculated data by Nielsen model and experimental data is unacceptable. The behaviors of the thermal conduction of TPI composites at the steady state could be simulated properly by FEM. Based on an analysis of the thermal flux in unit of composites, it is found that the influence of the filler thermal conductivity on the composites thermal behavior is not obvious, and the thermal conductivity of the composite with the rectangle filler is much higher than that with rotundity filler.