The traditional treatment of waste incineration flue gas is mostly carried out in low temperatures, but there are some problems such as corrosion of the heating surface at high and low temperatures, re-synthesis of dioxins, and low efficiency. Therefore, it is necessary to remove the pollutants at high temperatures. For the grate waste incinerator, this study proposes an adiabatic cyclone flue arranged at the exit of the first-stage furnace of the grate waste incinerator to pre-remove the fly ash at high temperatures, so as to alleviate the abrasion and corrosion of the tail heating surface. In this paper, computational fluid dynamics (CFD) method is applied to study the performance of a cyclone flue under different structural parameters, and the comprehensive performance of the cyclone flue is evaluated by the technique for order preference by similarity to an ideal solution (TOPSIS) method. The results show that particle separation efficiency increases at first and then decreases with the increase of the vortex finder length, the vortex finder diameter, and the distance between vortex finder and gas outlet tube, while it decreases with the increase of the gas outlet tube diameter. The pressure drop increases with the increase of the vortex finder length, and the vortex finder diameter, while decreases with the increase of the distance between the vortex finder, the gas outlet tube, and the gas outlet tube diameter. In the scope of this study, when h1/a = 1.1, D1/A = 0.33, h2/A = 1.5, and D2/A = 0.50, the comprehensive performance of the cyclone flue is much better.