Three kinds of rotating-stream tray（RST）separators were designed and designated as S1，S2 and S3.The separator S1 had double flow paths，while S2 and S3 had single flow path.The trays of S1 and S2 were the same of the double-path type，which was different from the conventional outward tray of S3.Measurements of three-dimensional flow in the three RST separators were conducted at the same total gas flow rate and streamlines were given through calculation according to the measured data.Compared with the RST separators S2 and S3，the separator S1 not only reduced the separation distance，but also effectively increased the tangential velocity，especially in the neighborhood of the separator center.The structure of tray vanes had a great effect on the velocity profiles，especially on the axial velocity profiles.The maximal axial velocities of S1 and S2 near the separator wall were much lower than that of S3.The maximal axial velocity of S1 decreased by above 37% against that of S3，which was favorable for reducing the secondary carry-over in the two-phase separation process.Streamlines showed that the separator S3 had vortex rings over the whole axial section，while the separator S1 had vortex ring only near the tray vanes.The separator outlet baffle could increase the tangential velocity，moderate the axial velocity，and reduce the centripetal velocity.