The effect of cyclone dimensions on separation performance is significant. An optimum cyclone height, so-called the maximum-efficiency cyclone height here, can make the efficiency of cyclone separator best. In this paper, the effect of inlet dimensions on the maximum-efficiency cyclone height is studied through experiments and CFD simulations. The experimental results indicate that the maximum-efficiency cyclone height reduces with the reduction of the inlet dimensions. CFD simulations suggest the natural vortex length shortens with the reduction of the inlet dimensions. There is a significant consistency between the changing trends of the maximum-efficiency cyclone height and the natural vortex length. Moreover, the increasing of the cone height brings about the extension of natural vortex length and results in the increase of efficiency. However, once the position of vortex end enters into the space of the cone, the separation efficiency turns to decrease. This phenomenon exists in all kinds of cyclones with different inlet dimensions. It suggests that the natural vortex length plays a significant role in determining the maximum-efficiency cyclone height, and the effect of the inlet dimensions on the maximum-efficiency cyclone height might be attributed to the effect of the inlet dimensions on the natural vortex length. (c) 2012 Elsevier B.V. All rights reserved.