A microstructural array to generate the interference of near-field vortex beams is designed, in which an Archimedean spiral line is formed by a pair of orthogonally arranged rectangular holes. Upon the excitation of a linearly polarized terahertz beam, the near field vortex beams with different topological charge numbers are formed by their left-handed and right-handed components and superimposed to generate a new field distribution. The numerical simulation results show that the field superposition of orthogonal vortex beams with arbitrary topological charge numbers can be achieved by the adjustments of the angle of each rectangular hole and the pitch of the helix.