The invention relates to a membrane bioreactor sewage treatment device, which is characterized in that a sewage inlet pipe (1) and a grille (2) are arranged in a regulation tank (14); a stirring rod (3) is arranged in an anaerobic tank (15); a sewage pump (4), a first sludge pump (6) and a first aeration plate (10) are arranged in a front aerobic tank (17); a second aeration plate (11), a second sludge pump (8) and a gas-water backflush plate (13) are arranged in a back aerobic tank (24); a membrane assembly (25) is arranged in the back aerobic tank (24), and is connected with a clear water tank (26) through a water outlet pipe (27); the gas-water backflush plate (13) is connected to a clear water pump (12) arranged in the clear water tank (26) through a clear water backflush pipe (28); and outlet water is collected in the clear water tank (26). According to the utility model, membrane pollution and washing frequency can be reduced, and membrane service life can be prolonged; sludge discharge amount is reduced; and the removal rate of phosphorous in the sewage is improved.