Abstract: At present, the determination of the structural parameters of none-pressure three-product dense medium cyclone mainly depends on the practical experi ence of coal preparation workers, which lead to insufficient accuracy. Based on the analysis of raw coal properties, the quantity and quality of each product are predicte d. The products' density and volume distribution of dense-medium suspension are considered. In combination with scientific experiments and related formulas in practic e, the structural parameters of none-pressure three-product dense medium cyclone are determined by calculation. Through comparison of calculation results and empiri cal formula, it is found that the diameter of the overflow section of the two stage cyclone is more accurate according to calculation of ( 0.20 ~ 0.45) do1 ( do1 is the diam eter of the overflow section of first stage cyclone)，which can provide a new idea for the determination of its parameters and the selection of equipment.