In　this　paper,　a　fiber　coupled-mode　equation　between　front-wave　and　back-wave　of　optical　guided　modes　with　micro　disturbance　is　given　from　parameter　interaction　equation.　Considering　surface　acoustic　wave　(SAW)　as　the　micro　disturbance,　a　coupled-wave　equation　group　of　SAW　all-fiber　acousto-optic　(AO)　effect　is　deduced.　The　equation　group　includes　front-wave　equation　and　back-wave　equation.　A　back-wave　efficiency　formula　is　demonstrated　through　solving　the　equation　group.　It　is　proved,　that　the　back-wave　efficiency　is　directly　proportional　to　power　of　the　SAW　under　condition　of　weak　AO　interaction.　Quartz　crystal　is　considered　as　the　best　base　crystal.　It　is　because　acoustic　impedances　of　the　quartz　crystal　and　the　fiber　are　equal　approximately.　According　to　form　of　SAW　basic　equations　or　Christofell　equations　the　best　SAW　mode　of　the　quartz　is　determined.　All-fiber　AO　intensity　modulator　using　SAW　is　designed　and　manufactured.　Modulation　curve　of　optic　power　of　the　back-wave　vs　power　of　electric　signals　driving　the　device　is　measured.　The　experimental　results　indicate,　optic　power　of　the　back-wave　is　directly　proportional　to　power　of　electric　signals　driving　the　device.　The　experimental　results　are　consistent　with　the　theory.　Advantages　of　the　device　are　smaller　volumes,　less　energy　consumes,　less　inset-losses　and　so　on.　Besides,　it　is　easy　to　integration　and　can　be　used　in　optic　fiber　communication.