The gas-solid flow behavior and dust distribution in four rough-cut cyclones was numerically simulated on the platform of FLUENT 6.2. The Reynolds stress model and stochastic particle tracking model were used to describe the gas flow and particle motion. The calculation results indicated that the particle distribution patterns of the four rough-cut cyclones were similar. Adding solid particles into the gas phase weakened the gas swirling intensity inside the cyclones. Data of rough-cut cyclone down-flow ratios were gained by simulation for the first time. Rough-cut cyclones with wider diplegs were found to have a massive gas down-flow through the dipleg which might cause serious coke generation inside the disengager. The simulated cyclone structure with its vortex finder wider than the dipleg and a hopper installed behaved the best. The results may provide indications for industrial anti coke research and rough-cut cyclone design.