Abstract: In order to see the transmission of electromagnetic wave in photonic crystals,the finite difference time domain method was used to calculate the band gap of two-dimension photonic crystals,and with the help of MATLAB,it could make the transmission of the electromagnetic wave in the vacuum and photonic crystals visual.At the meantime,the static map was shown.Numerical analysis showed that the wave in the forbidden band was controlled in photonic crystals,and its energy distributed in the media rod nearby,the localization of electromagnetic was observed.