Abstract: In this paper,the setup method of the PML boundary parameter for FDTD technique which has widely used in electromagnetic propagation problems is considered.A new setup method of the PML boundary parameter is proposed for FDTD technique.The conductivity of the absorb boundary are obtained by means of reflection error is minimized by GA in the same source.The best conductivity values which can minimize the boundary reflection error in the same source.The reflection error of the best conductivity is less 3~4 times than the common values.So the setup method of the PML boundary parameter can enhance electromagnetic calculate precision.