Abstract: The vortex structures of round turbulent jets in cross-flow with different velocity-ratio were investigated by using the PIV in this paper.It is found that the vortex structures include the Kelvin-like vortexes in shear-layer of jet,the cross-flow separation vortex pair,the horseshoe vortex system in upstream bottom region of jet and the wake vortexes.Through analysis of evolvement mechanism of vortex structure and topology,the two separation lines in the nearfield of the jets are obtained :one of them is the separation line of the cross-flow and another is the line of shear vortexes around the jet to enter cross-flow separation vortexes.Ultimately,the separation vortex pair enter and mix with the jet at far field to form the counter-rotating vortex pair in the jet body.