The terahertz (THz) field can be confined and manipulated at the sub-wavelength level using spoof surface plasmon polaritons (SSPPs) formed on structured metal/dielectric interfaces. Furthermore, it is feasible to manipulate THz waves on a two-dimensional (2D) scale by utilizing the dispersion properties of the unit structure on the geometrical parameters, which provides a solution for the development of integrated and miniaturized on-chip THz multi-functional devices. This study proposes a 2D gradient refractive index lens based on the dispersion characteristics of the metallic pillar structure. THz SSPP devices were designed according to the proposed design scheme for manipulating the propagation, such as flat telescopes, waveguide couplers, and dual-function lenses, and the working performance of each functional device was analyzed through electromagnetic simulations. This study not only enhances the different THz surface wave control devices but can also help develop THz on-chip systems further based on surface plasmon polariton chains.