The migration equation of fluorine in polycrystalline silicon gate is presented on the basis of analysis for the migration characteristics of fluorine in polycrystalline silicon gate after BF+2 is implanted into polycrystalline silicon gate.The distribution of fluorine in polycrystalline silicon gate is simulated by the finite difference methods.The simulation results are in good agreement with the experiments.Under the condition of 80keV,2×1015cm-2BF+2 implanted into polycrystalline Si gate and then annealed at 900℃ for 30s,some important coefficients are given as follows: emisson coefficient of fluorine in polycrystalline silicon e=6×10-2s-1,diffusion coefficient of fluorine in grain boundary Db=7.64×10-12cm/s,absorption coefficient of fluorine in polycrystalline Si/SiO2 interface S1=1.74×10-3s-1 and damage absorption coefficient of fluorine in polycrystalline silicon S1=7.32×10-4s-1.