The　skin　friction　consumes　some　of　the　energy　when　a　train　is　running,　and　the　coherent　structure　plays　an　important　role　in　the　skin　friction.　In　this　paper,　we　focus　on　the　coherent　structure　generated　near　the　vent　of　a　train.　The　intention　is　to　investigate　the　effect　of　the　vent　on　the　generation　of　coherent　structures.　The　ventilation　system　of　a　high-speed　train　is　reasonably　simplified　as　a　T-junction　duct　with　vertical　blades.　The　velocity　signal　of　the　cross　duct　was　measured　in　three　different　sections　(upstream,　mid-center　and　downstream),　and　then　the　coherent　structure　of　the　denoised　signals　was　analyzed　by　continuous　wavelet　transform　(CWT).　The　analysis　indicates　that　the　coherent　structure　frequencies　become　abundant　and　the　energy　peak　decreases　with　the　increase　of　the　velocity　ratio.　As　a　result,　we　conclude　that　a　higher　velocity　ratio　is　preferable　to　reduce　the　skin　friction　of　the　train.　Besides,　with　the　increase　of　velocity　ratio,　the　dimensionless　frequency　St　of　the　high-energy　coherent　structure　does　not　change　obviously　and　St　=　3.09　×　10＜sup＞−4＜/sup＞–4.51　×　10＜sup＞−4＜/sup＞.View　Full-Text