The　modal　analysis　of　pipes　conveying　fluid　considering　the　influence　of　Fluid-Structure　Interaction　(FSI)　is　always　a　topic　in　flow　and　solid　mechanics　fields　worth　study.　Three　methods　of　coupling,　the　direct　FSI　method,　the　one-way　FSI　method　and　the　bidirectional　FSI　method,　with　the　velocity＇s　influence　on　pipe　system＇s　natural　frequency　were　considered　in　this　study.　The　results　of　pipe＇s　dynamic　behavior　indicate　that　the　two-way　FSI　method　can　get　a　more　reasonable　result.　Furthermore,　when　velocity　changes　in　a　small　range　far　from　critical　velocity,　velocity　makes　very　little　influence　on　system＇s　nature　frequency.　The　result　was　compared　with　conclusion　in　the　literature　and　very　good　agreement　was　found.