A new method for predicting the thermal conductivity of functional carbide crystals and ceramics materials is proposed. The effect of average relative atomic mass and density on thermal conductivities of carbide function crystals and ceramics is considered in the method. Correlations are developed for thermal conductivity with average relative atomic mass and density according to the microscope theories of heat conduction. The thermal conductivities calculated from the prediction equation for many functional carbide crystals and ceramics were compared with the measured dada and found to be agreement. It is show that, for the most of functional carbide crystals and ceramics materials, the relative error between the predicting values and the measuring data is ± 20%. It is discovered in further analysis that the larger the average relative atomic mass and density are, the more accurately the thermal conductivities predict.