Abstract: The constitutive equation of dust suppression foam yields to the generalized Bingham fluid model. In order to improve the coverage efficiency and the utilization ratio of the foam, the out flow field of the foam from the flat-fan nozzle has been studied by means of numerical simulation and experiment. Based on this study, the opening structure on both sides of the flat-fan nozzle puts adverse effects on the coverage efficiency. The effective angle and the effective length are defined for the quantitative analysis, and the results suggest that the optimum foam velocity at the inlet of the flat-fan nozzle is 3 to 5 m/s.