Abstract: Bubble size is an important basis to estimate the flotation kinetic process and separation effect.The impeller working parameters fundamentally determined the size of fluid flow passage and the characteristics of fluid, and then affected the bubbles dispersion and the particles suspension.In this research, a high-speed camera is used to shoot the bubbles and analyze bubbles size in a KYF flotation machine, and the interaction effects of two factors in impeller diameter, off-bottom clearance of impeller and impeller speed on bubbles size distribution are systematically examined.The results show that increasing the impeller diameter, reducing the off-bottom clearance of impeller and increasing the impeller speed all can reduce bubbles size and improve the uniformity of bubbles size distribution.There are some significant synergistic interactions between impeller speed with impeller diameter and off-bottom clearance of impeller.At a lower or medium impeller speed (300-400 r/min), impeller structure parameters are of more significant importance in regulating bubbles size characteristics.However, the effect of impeller speed is more remarkable at a small impeller diameter (150 mm) or a large off-bottom clearance of impeller (32-36 mm).Regarding the two structural parameters of impeller, the effect of impeller diameter on bubbles size is more significant than that of the impeller off-bottom clearance.Moreover, the interaction between them is also certain.The larger the impeller diameter is, the more obvious of the effect of the impeller off-bottom clearance on the uniformity of bubbles size.The results can provide some basis for the selection of impeller size and installation operation parameters in the flotation machine.