The invention discloses a rapid chemical mixing device for oil field sewage treatment. The rapid chemical mixing device comprises a mixer, an aeration tube and a separation tank which are connected insequence, wherein the mixer comprises a conical rotational flow cavity and a small mixing tube; the small mixing tube is inserted into the conical rotational flow cavity from the upper end; the upperend of the small mixing tube is connected with a gas tube and a chemical tube in parallel respectively; a sewage inlet is formed in the side wall of the upper end of the conical rotational flow cavity; and the aeration tube is connected with the lower end of the conical rotational flow cavity through a mixing outlet. At least one mixer is used, if multiple mixers are used, the mixers are connected in a serial connection manner, that is, the mixing outlet of a former mixer is connected with the inlet of the conical rotational flow cavity of a next mixer, and the mixing outlet of a last mixer is connected with the aeration tube. Due to dual effects of negative pressure sucking and rotational flow mixing, chemicals can be uniformly and rapidly added, the mixing reaction time is shortened, the chemicals can be saved, miniaturization of equipment is achieved, and the rapid chemical mixing device has great significance for oil field sewage treatment.