Scattering matrix method is a research method in frequency domain. Transmission spectra of metal films with periodic air holes is studied based on this method. Copper slabs etched with periodic square lattice of air holes are used. Lorentz-Drude model is used to describe permittivity ε of copper. Transmission spectra are obtained for different thicknesses of copper slabs, different lattice constants and different radii of air holes. The results agree well with the results obtained by finite-difference time-domain method (FDTD). It is shown that while light cannot be transmitted thought metal slabs, extraordinary optical transmissions can be observed if metal slabs are drilled with periodic air holes. This is mainly caused by surface plasmon resonance in the metal photonic crystal slabs. Results can be verified by comparing them obtained from the scattering matrix method in frequency domain and the FDTD method in time domain. Thus it can reduce the cost to verify the results experimentally and enhance the ability of simulation.