The utility model relates to a reactor mixing impeller during continuous spandex polymerization production. The reactor mixing impeller comprises multiple mixing blades which are uniformly distributed in a radial shape; multiple grooves are formed in the working faces of the mixing blades; the multiple grooves are radially distributed along the mixing blades by taking the rotating center of the mixing impeller as a rotating center; the groove widths of the grooves are increased along with increase of the diameter of a circumference on which the grooves are positioned; and the groove depths of the grooves are reduced along with increase of the diameter of the circumference on which the grooves are positioned. When mixing operation is performed by using the mixing impeller with the structure, the materials are fully mixed, mass transfer is reliable, and regular fluctuation of the viscosity of the materials is eliminated, so that a good mixing effect is obtained, the reaction efficiency is improved, the reactant retention time is shortened, and the daily production capacity of the reactor is improved.