The impeller of the flotation machine comprises a cover plate, blades and an air outlet flow guide body, the air outlet flow guide body is arranged at the upper position of the center of the impeller,the inner side edges of the blades are fixedly connected with the side walls of the air outlet flow guide body, the cover plate is arranged above the blades and fixedly connected with the upper edgesof the blades, and the outer surface of the whole impeller is coated with a wear-resisting layer. The upper portion of the air outlet flow guide body is a hollow cylinder, the lower portion of the air outlet flow guide body is of a hollow or solid cone structure or a semi-circular structure, the framework material in the lower area of the outer side edge of the blade is sunken inwards, and the sunken portion is filled with a wear-resisting layer. The rotary surface of the outer side edge of each blade is of a double-inverted-cone structure, and the blades incline backwards by 15-75 degrees inthe radial direction. The large-torque gas-liquid separator not only meets the gas-filling stirring requirement, but also has enough strength, supports large-torque output, is low in operation powerconsumption and good in separation performance, and meets the application requirement of an ultra-large flotation machine.