The characteristics of EM in dielectric-metal-dielectric (MDM) surface plasmon polaritons (SPPs) waveguides were presented. The numerical results show that the waveguide can only excitate the first order SPP mode (fundamental mode) for the wavelength of 633 nm, if the dielectric film thickness is less than 85 nm. With the dielectric film thickness increasing, progressively high order SPP modes are excited. The real part of the effective refractive index decreases with increasing the order of the SPP modes, but that of the imaginary part shows an opposite trend. However, when the dielectric layer of the MDM waveguide thickness is more than 0.555 μm, since the third-order mode of the electromagnetic field SPP concentrated in relatively distant from the metal layer, the effective refractive index has a minimum value of the imaginary part. So the third-order SPP mode has a maximum propagation distance. When the wavelength of the incident light is 633 nm, the dielectric layer thickness is 0.9 μm Ag/SiO2 /Ag, the transmission distance of the third-order SPP mode is about 150 μm in the waveguide.