Surface plasmon polaritons(SPPs)have some characteristics such as optical field localization and local electromagnetic field enhancement and so on, so it exhibits extensive potential application in nano-photonics and microscopic detection and many other domains.The finite-difference time-domain(FDTD)numerical method can simulate the surface plasmon(SP)effect of laser interaction with the subwavelength metal mi-crostructure.The relative dielectric constant of metal is frequency dependent(dispersion).There are three dis-persion models about metal's relative dielectric constant in visible light and near-infrared wave band, such as Drude model, Lorentzs model and Drude-Lorentzs mode.In order to get FDTD iterative computation stable, FDTD numerical method should increase the subsidiary variable and the corresponding auxiliary difference equa-tion.