The invention discloses a sewage biological treatment method and a sewage biological treatment device for changing microbial quality. The sewage biological treatment device comprises a water inlet tube, a regulating tank, a microbial modifying tank, an anoxic hydrolyzing tank, a primary baffling aerobic tank, a secondary baffling aerobic tank, a water outlet tube and the like. The sewage biological treatment method comprises the following steps of: firstly, adding microbial modifying flora into a device and regulating; then, passing to-be-treated sewage and wastewater through the water inlet tube, the regulating tank, the microbial modifying tank, the anoxic hydrolyzing tank, the primary baffling aerobic tank and the secondary baffling aerobic tank in sequence, and discharging the sewage and wastewater after the sewage and the wastewater are qualified through a series of biological chemical reactions. According to the sewage biological treatment method and the sewage biological treatment device for changing the microbial quality disclosed by the invention, the leading-in of the microbial modifying strain and the sewage and wastewater treatment process are combined, so that the technical advantages such as strong capacity of degrading organic substances on engineering, complete decomposition, small mud producing factor, strong high load resistance, strong toxic substance impact resistance and low operation cost are achieved.