The　capillary　jet　break　up　into　a　train　of　drops　with　artificial　perturbation,　which　can　be　applied　into　many　fields.　Due　to　the　small　dimension　and　high　velocity　of　the　jet,　especially　for　the　jet　in　other　liquid,　it＇s　very　difficult　to　trackle　the　detail　of　the　jet　breakup.　In　this　study,　with　the　help　of　the　dynamic　mesh　method　and　Volume　of　Fluids　(VOF)　method,　the　whole　process　including　the　application　of　the　perturbation　to　the　jet,　jet　breaking　up　into　droplets,　and　droplets　falling　in　the　oil　was　simulated　by　the　computational　fluid　dynamics　(CFD)　software　FLUENT.　The　effect　of　perturbation　frequency　on　the　Sn-Bi　jet　breakup　in　silicon　oil　was　studied.　The　results　show　that　the　fluctuation　of　jet　velocity　is　found　to　account　for　the　presence　of　necking　of　jet.　With　the　increasing　of　the　perturbation　frequency,　the　diameter　of　the　droplet　decreases.　The　jet　breakup　length　is　the　shortest　when　the　optical　perturbation　frequency　is　applied,　and　the　numerical　results　agree　well　with　the　experimental　ones.