In this paper，we show that the enhanced transmission and the surface plasmon distribution through a thin gold film with a periodic array of subwavelength holes with the finite-difference time-domain (FDTD) method. The transmission spectra exhibit two different surface plasmon resonance features: the localized waveguide resonance and the well-recognized photonic crystal resonance. For the localized waveguide resonance，the tangential electric field component Ey is seen to be concentrated entirely in the rectangular air hole region. And for the photonic crystal resonance，the tangential electric field components Ey is nonzero only on the two sides of the rectangular hole region. With the aid of the SP，light can form a strong focal spot at the bottom of the metal.