The invention discloses a sewage treatment mixer. The sewage treatment mixer is characterized by comprising a dual-output shaft motor (5), transmission shafts (3) arranged at the two output shaft ends of the dual-output shaft motor (5), bearing seats (4) arranged at the peripheries of the transmission shafts (3), a mechanical sealing seat (2) for preventing sewage from flowing into an inner cavity of the mixer, an impeller A (1) and an impeller B (6), wherein the impeller A (1) and the impeller B (6) are located on the two sides of the dual-output shaft motor (5), are connected with the transmission shafts (3), and have the same shape and size and opposite torsion direction. According to the invention, the mixing requirements can be met by mounting one sewage treatment mixer in a big water pool only.