Abstract: The feed dust concentration has an important influence on the separation efficiency and pressure drop of cyclone. In the range of dust concentration of 5~550 g/m3, the separation efficiency of 500mm diameter PV cyclone with three different exit tubes was investigated using 325 mesh talcum powder. The exit tubes with small cylindrical (type A), cone (type B) and big cylindrical (type C) were used, respectively. The experimental results show that the separation efficiencies go up with increasing dust concentration in feed. However the separation efficiency increases smoothly when the feed concentration is above 150 g/m3. With increasing the feed concentration, the tangential velocity decreases and thereby the separation ability decreases. As the aggregation between particles increases, the inertia separation ability rises, resulting in improved separation efficiency but more particles escaped. The experimental results also show that the exit tube structure of cyclone separator, especially the diameter, has a considerable effect on separation efficiency. Finally, according to the experiment date and considering the influence of inlet feed velocity and exit tube diameter, an empirical equation for calculating separation efficiency of cyclone is given.