The method of the dielectric loaded is presented to obtain low loss in propagation of the surface plasmon polaritons (SPPs). Comparing the conventional insulator-metal-insulator (IMI) waveguide and the waveguide with dielectric loaded, it is demonstrated that the method of dielectric loaded can reduce the loss in propagation and achieve smaller group velocity. A silica layer between a silver film and silicon layer is employed to improve the propagation performance of SPPs in the“trapped rainbow”system based on graded grating structure. Time domain finite difference simulation demonstrates that the improved structure is able to localize light of different frequencies at different positions and offers the advantage of supporting slow SPPs with a much lower propagation loss and deeper sub-wavelength confinement. The proposed structure has a wide range of applications in optical processing and optical communication.