Abstract: Flow visualization test of swept wing/body junctions has been performed with laser light sheet technique and sodium-fluorescence dyed liquid method in the water channel of BUAA. The results show that in addition to Reynolds number, the angle of attack and the swept angle are also very important parameters that influence the horseshoe vortex characteristics in the juncture zone. It is found that there exists a new kind of 3-D steady vortex system——back vortex, which is different from the horseshoe vortex and the Karman vortex. The back vortex exists for both swept cylinder and swept wing conditions. It comes from the rear part of the junctions and extends into space. The back vortexes will breakdown under certain angle of attack and the swept angle. The characteristic of swept wing back vortex is different from that of swept cylinder back vortex. The forming mechanism of this back vortex system and its relationship with horseshoe vortex system are also discussed. Finally, some typical sections of the junctions have been measured using PIV technique.