The　spoof　surface　plasmon　polariton　(SPP)　effect　on　the　electromagnetic　field　distribution　near　the　tip　of　a　periodically　corrugated　metal　cylinder-cone　probe　working　at　the　terahertz　regime　was　studied.　We　found　that　radially　polarized　terahertz　radiation　could　be　coupled　effectively　through　a　spoof　SPP　into　a　surface　wave　and　propagated　along　the　corrugated　surface,　resulting　in　more　than　20x　electric　field　enhancement　near　the　tip　of　probe.　Multiple　resonances　caused　by　the　antenna　effect　were　discussed　in　detail　by　finite　element　computation　and　theoretical　analysis　of　dispersion　relation　for　spoof　SPP　modes.　Moreover,　the　key　figures　of　merit　such　as　the　resonance　frequency　of　the　SPP　can　be　flexibly　tuned　by　modifying　the　geometry　of　the　probe　structure,　making　it　attractive　for　application　in　an　apertureless　background-free　terahertz　near-field　microscope.　(C)　2014　Optical　Society　of　America