Optical　tapered　fiber　is　one　of　the　most　high　efficiency　evanescent　wave　coupler　for　coupling　light　into　and　out　the　optical　microcavity.　We　fabricated　the　tapered　fiber　with　etching　method　in　a　designed　groove　with　HF　solution.　This　method　was　low　cost,　readily,　and　controllable.　An　etching　groove　had　an　oval　in　the　middle　and　small　V-shape　towards　both　sides.　HF　solution　was　injected　into　the　oval　groove,　while　the　deioned　water　was　injected　into　the　two　V-grooves.　Because　of　the　solution　diffusion,　the　etching　rate　was　fast　in　the　mid　and　decreased　gradually　towards　both　sides,the　tapered　fiber　was　fabricated.　The　optical　power　meter　was　monitoring　the　fiber　transmission　during　the　etching　process.　The　transmission　of　the　tapered　fiber　was　98%.　We　proposed　a　mathematics　model　to　depict　the　etching　process,　containing　the　relationship　between　the　diameter　of　tapered　fiber　and　the　concentration　of　the　HF　solution,　the　etching　time,　humidity,　temperature.　We　supervised　the　optical　intensity　to　deduce　the　tapered　fiber　diameter.　Surface　morphology　with　AFM　was　detected,　the　roughness　of　the　tapered　fiber　surface　is　less　than　1nm.　As　an　evanescent　coupler,　we　used　the　tapered　fiber　to　transmit　980nm　pump　laser　to　couple　to　Er3+　doped　microsphere　to　stimulate　1557nm　laser.