The invention relates to the technical field of sewage treatment and particularly relates to an A3 / O-MBBR (Moving Bed Biofilm Reactor) integrated sewage treatment device and an A3 / O-MBBR integrated sewage treatment method. According to the device provided by the invention, a sewage backflow mechanism, a nitrification liquor backflow mechanism and an anaerobic liquor backflow mechanism are arranged and suspended filler is filled in an aerobic tank, so that the integrated sewage treatment device has a good effect for treating nitrogen and phosphorus in sewage and is high in treatment efficiency, compact in structure and small in occupied area. In addition, by virtue of optimizing a settling pond structure in the integrated sewage treatment device, the settling effect of the settling pond is improved, and the sludge floatation phenomenon and the content of suspended solids in effluent can be remarkably reduced. After sewage is treated by the integrated sewage treatment device provided by the invention, the effluent can reach the level A of first class stand of pollution discharge standard for municipal sewage treatment plant (GB18918-2002).