In　order　to　study　fluid　flow　characteristics　of　the　micro-nano　gap,　the　boundary　slip　in　micro-nano　gap　was　studied　using　atomic　force　microscope,　mainly　from　the　standpoint　of　liquid　viscosity.　The　solid　sample　was　SiO2,　the　liquid　sample　was　pentarythriol　oleate　with　different　viscosity,　their　molecular　formula　are　C77H140O8,　their　viscosity　were　32　mm2/s　and　150　mm2/s,　respectively.　Using　the　relative　velocity　method　processed　the　test　results,　as　the　results　shown,　two　different　types　of　pentaerythritol　oleate　on　the　face　of　SiO2　both　have　boundary　slip,　the　boundary　slip　increases　with　increasing　of　liquid　viscosity.　The　reason　is　shown　as　follow,　with　the　viscosity　increasing,　the　shear　force　which　will　increase　between　nearing　the　solid　surface　liquid　molecules　and　contacting　with　solid　surface　liquid　molecules,　so　that　solid-liquid　force　is　easy　to　overcome,　easy　to　generate　boundary　slip.　©,　2015,　China　Mechanical　Engineering　Magazine　Office.　All　right　reserved.