Terahertz (THz) scattering-type scanning near-field optical microscopy (THz s-SNOM) is an important means of studying and revealing material properties at the nanoscale. Nanotip is one of the core components of THz s-SNOM, which has a decisive impact on the resolution of the system. This paper focuses on the theory and design of nanotip, and conducts comprehensive research on it through simulation. The theoretical model is based on full wave numerical simulation and dipole moment analysis which can describe the overall nanotip electromagnetic response under the incident field. A comprehensive design model of nanotips’ geometry, sample materials, and incident field is established to significantly improve the near-field couple efficiency and spatial resolution to achieve optimal performance.