Abstract: Numerical simulation is made of the prototype XJM-S45 flotation machine using CFC software. The characteristic parameters of the flow field at different impeller structural and running parameters are calculated. According to the variation of the characteristic parameters like impeller's fluid displacement and power in relation to the impeller's structural and operating parameters, the optimum impeller parameters as follows are determined, thus realizing the structural optimization of the impeller of the XJM-S45 flotation machine: speed-136 r/min; number of blades-8; back inclination angle of lower blade-5 degrees larger than the original design.