Metal grating models are designed to correspond the extraordinary transmission, structures with single slit and periodic slits and structures with different widths and different periods are calculated by finite difference time domain (FDTD) method. It is found that grooves on a metal grating play a negative role to energy transfer on the metal surface. Frequency domain of transmission becomes wider in pace with the width of the film; with the increasing of the width of the slit, the distribution envelope tends to flat, the side of shorter wavelength of the main transmission peak is essentially the same, while the distribution curve of the main transmission peaks and the side of longer wavelength of it become wider. It indicates that the width of the slits impacts the resonance modes of surface and the distribution of transmission. The transmission of single slit compared to the periodic structure′s, we found that transmittance curves almost coincide. It shows that the surface modes do not depend on the slits and there is no interaction between them.