The invention discloses a method for intensifying a phosphorus removing effect of a membrane bioreactor through water supply plant dewatering sludge, relates to the sewage treatment phosphorus removing technology and is applicable to removing of phosphorus left in outlet water of the membrane bioreactor process. According to the method, a water supply plant granulation water purification sludge phosphorus removing device is combined with the membrane bioreactor and a flat sheet membrane concentration digestion tank to conduct sewage treatment, and phosphorus removing of the outlet water of the membrane bioreactor is intensified so that the outlet water can be drained after reaching a standard of drainage. The advantages that the water quality of the outlet water of the membrane bioreactor is stable, the water supply plant granulation water purification sludge is good in phosphorus removing effect and large in adsorption capacity, saturation sludge treatment is convenient, and the flat sheet membrane concentration digestion tank efficiently treats the biological sludge are fully utilized, efficient resource integration and utilization and membrane bioreactor treatment optimization are achieved, great manpower, material resources and running management cost are saved, the running management efficiency is improved, and the method has good economic benefits and social benefits and has wide application prospects especially in the field of distributed type sewage treatment.