The invention discloses an A / O integrated membrane biological treatment device based on microanaerobic sludge quantity and a method for treating sewage by using the device, and relates to the field of sewage treatment. The device comprises an aerobic zone, a micro sludge quantity anaerobic zone, a precipitation tank, an aeration tray, a membrane module, an electric flocculation device, a sewage buffer storage tank, a purified water storing tank, a water-charging pump, an aeration pump, a circulating pump, a reflux pump and a self-priming pump. A use method comprises the following steps: firstly, opening the aeration pump and an aeration valve for continuously aerating; secondly, filling the aerobic zone with activated sludge, performing nitration reaction treatment, performing denitrification reaction on the micro sludge quantity anaerobic zone, removing phosphorus by the electric flocculation device, removing phosphorus by the membrane module in an intensified manner, and removing nitrogen and small particulate matters. The device disclosed by the invention also has the characteristics of small occupied area, convenience in use, high treatment efficiency and the like, and is more suitable for being installed and used on a ship; the device accords with or is superior to discharge standards, stipulated by a new IMO convection, of domestic sewage in nitrogen and phosphorus effluent indicators. The device and the use method thereof disclosed by the invention are suitable for treating sewage.