Indium tin oxide (ITO), as a kind of transparent optic glass, is a highly degenerate semiconductor. The dielectric constant of ITO changes with incident wavelengths and is complex number. Ag-ITO-Ag waveguide is designed by ITO as dielectric layers. The transmission characteristics of electromagmetic waves in the structure of surface plasmon polariton (SPP) waveguide and the relevant characteristic parameters of SPP are obtained. In this structure, the expression of magnetic field distribution, SPP′s wavelength, propagation distance and dispersion equation are derived and the dispersion characteristic is researched. Besides, the relationship between group velocity and incident wavelength is studied. The effects of the thickness of dielectric layer on group velocity, different core mediums (ITO, air, SiO2) of the structure with same cladding layers (Ag) on group velocity and slow light effect are discussed. The results show that the Ag-ITO-Ag waveguide structure is more favorable for miniaturization and integration of photonic devices.