The purpose of this paper is to study the effects of a secondary flow injection method on sub-micron particle separation in a new type of gas-cyclone. it was found that particle collection efficiency and classification accuracy of the improved type cyclone was higher than that of the original type cyclone. Three-dimensional simulation results of the improved type cyclone indicated increased fluid rotational velocity in the cylindrical part and increased downward velocity in the conical part compared to the original type cyclone. Experimental results qualitatively agree with the numerical simulation. In order to improve high particle separation performance of gas-cyclones, it is recommended to use both the secondary flow injection and inlet guide plate methods. (C) 2009 Published by Elsevier B.V.