This paper presents a numerical study of the gas liquid solid flow in 1000 mm dense medium cyclones (DMCs) with different body dimensions, which includes the spigot diameter, cylinder length, cone length and inlet size by means of a computer model which we recently proposed. In this model, mixture multiphase model is used to describe the flow of the dense medium (comprising finely ground magnetite contaminated with non-magnetic material in water) and the air core, where the turbulence is described by the well-established Reynolds Stress Model. The stochastic Lagrangian Particle Tracking method is used to simulate the flow of coal particles. It is found that the spigot size is very sensitive to the performance. The operational head and medium split reporting to overflow, decrease dramatically as the spigot diameter increases. The density differential decreases rapidly, and then passes through a minimum and increases slowly. The long body including cylinder and cone is helpful to particle separation, particularly for fine and heavy particles. The inlet size plays a remarkable role on the performance on DMCs. The operational head, the density differential and the medium split increase dramatically as the inlet size decreases. Both the upward flow and the downward flow become very strong in the DMC with a small inlet when medium feed rate is constant, which results in a very low Ep. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.