The permittivity of carbon fibers in different composites is calculated and discussed by using M-G equations, Bruggeman equations and generalized M-G equation. Results show that for high draw ratio fibers, all the three equations can calculate out the permittivity with the same numerical level and variation trend. Generalized M-G equation and M-G equation have a similar result but Bruggemaris result is smaller. All three equations become invalidation when fibers' concentration reaches its percolation threshold, which means that all three equations are useful at low concentration.%采用M-G方程、Bruggeman方程和广义M-G方程计算了复合材料内碳纤维的介电常数.结果表明:当纤维长径比较大时,3个方程均可以计算出碳纤维的介电常数,并且数量级和趋势保持一致；广义M-G和M-G方程的计算结果较为一致,而Bruggeman方程则小于其余两者的计算结果；当碳纤维浓度上升至渗流浓度附近时,3个方程计算结果均出现一定程度的偏离,表明3个方程均适用于低浓度情况.
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