The invention discloses a mixed metal-dielectric SSP (Spoof Surface Plasmon) periodic grating system as well as application and a method thereof. By adopting a mixed metal-dielectric SSP periodic grating, the technical advantages of the existing SSP periodic metal waveguide can be adopted, and near-field propagation of terahertz wave can be limited more effectively by dielectric filling, so that the system has the characteristic of low loss; external electron beams excite surface plasmon polaritons on the mixed metal-dielectric SSP periodic grating, so that efficient spoof surface plasmon polaritons can be obtained under the condition that the SSP dispersion is matched with the dispersion of the external electron beams; moreover, a periodic metal-dielectric surface is formed by dielectric filling, so that the spoof surface plasmon polaritons can be limited more effectively relative to a pure metal periodic grating; meanwhile, an implementation diagram of the system principle of electron beam excited SSP is given, so that the defect of low-power excitation in the existing optical excitation mode can be overcome, and the system has the characteristics of high power and high efficiency.