Abstract: A novel source formulation is proposed for the analysis of microstrip problem by using PML-FDTD(perfectly matched layer-finite difference time domain) method in this article.Unlike traditional treatment,only an electric current source is set without the corresponding magnetic current source.So there is no need to divide the field zone and set up the boundary connection condition at the excitation plane.This formulation is based on PML absorbing boundary condition and transparent current source.We applied this method to two cases: 1.uniform substrate;2.photonic crystal substrate.Numerical results agree well with theory.This method also can be used to analyze the characteristics of microstrip discontinuities.