Experimental and simulation studies have been conducted about the cut size control with revised dry cyclones. New type of dry cyclone with the apex cone which is covered with special ring indicated cut size movement from 2 to 40 mum. By use of the apex cone at the inlet of dust box, it is possible to decrease the fluid velocity component in the dust box and to reduce re-entrainment of particles from the dust box. The cut size indicates a minimum value for the specific height of the apex cone. The optimum apex cone height changes to the lower position as the cyclone inlet velocity increases. When the apex cone is set to high position, resistance for incoming particles entering to the dust box increases. The low apex cone position induces strong upward fluid flow component and number of escaping particles from the dust box increases. The experimental data agreed with the numerical simulation based on the three-dimensional direct flow calculation method.