Diffraction　limit　has　been　the　constraint　of　the　nanostructure　fabrication.　Because　the　scanning　near-field　optical　microscopy　(SNOM)　can　work　in　the　evanescent　near-field　region,　its　application　in　nano-processing　has　received　extensive　attention　from　researchers　globally.　In　this　paper,　we　combined　nanosecond　laser　with　cantilevered　SNOM　probe.　Utilizing　the　high　precision　of　the　confinement　and　enhancement　effect　of　probe　tip　and　the　high　instantaneous　energy　of　the　laser,　we　realized　nanostructure　fabrication　and　in　situ　detection　on　Au　nano-film.　Feature　sizes　down　to　47　nm　full　width　at　half　maximum　were　fabricated.　We　investigated　the　laser　propagation　through　the　SNOM　tip　aperture　and　the　light　field　intensity　distribution　on　the　surface　of　substrate　theoretically.　The　calculation　results　demonstrate　that　the　laser　is　highly　restricted　within　the　SNOM　aperture　and　enhanced　on　the　exit　plane　at　the　rim　of　aperture.　After　the　transmission,　the　light　field　intensity　distribution　on　the　surface　of　the　Au　nano-film　was　enhanced　due　to　the　localized　surface　plasmon　resonance.　The　thermal　distribution　on　the　surface　of　Au　nano-film　indicates　that　the　peak　of　the　temperature　distribution　appeared　at　the　surface　right　underneath　the　center　of　the　aperture.　It　is　proved　that　the　simulation　results　are　consistent　with　the　experimental　results.