The influence of the bottom-contracted and edge-sloped vent-pipe on the separation efficiency and pressure drop of a cyclone separator under different vent-pipe insert depth and different orientation of the sloped edge were studied in a visual cold circulating fluidized bed (CFB) experimental setup according to a commercial 100 MW CFB boiler with a scale of 20: 1. And the correlative results were also compared with the traditional linear-pipe-shaped cyclone separator. Results indicate that the cyclone inlet stream velocity has a strong influence on the separation efficiency and pressure drop, and the results are similar to that of the conventional cyclone. Namely, both separation efficiency and pressure drop increase with increasing cyclone inlet stream velocity. The separation efficiency of the modified cyclone separator increases firstly and then decreases with the increasing of the vent-pipe insert depth. However, there is not a very clear rule of the effect of vent-pipe insert depth on the pressure drop for modified cyclone separator. Both the separating efficiency and the pressure drop change with the orientation of the sloped edge, and they have the same rule of change, the maximum at 90 degrees and the minimum at 270 degrees. Due to the configuration of the bottom-contracted and edge-sloped vent-pipe is suitable with the flow field inside cyclone separator, the separation efficiencies of the modified cyclone separator are usually higher than those of traditional cyclone separators. (c) 2006 Elsevier B.V. All rights reserved.