The invention discloses an improved method for treating urban sewage. The method is a sewage treatment method improved on the basis of an oxidation ditch process, and comprises the following steps: reconstructing an anoxic zone in the oxidization ditch process into a mixed water distribution zone, wherein a BBR contact body device is arranged in the mixed water distribution zone; and reconstructing an aerobic zone into a biochemical zone, wherein a flora with bacillus microorganisms as a dominant strain exists in the biochemical zone. By applying the technical scheme of the invention, the method can achieve the following beneficial effects: (1) efficient denitrification and dephosphorization capacities; (2) no need of an additional deodorizing system; (3) great reduction of the reconstruction cost; (4) energy conservation, and no need of new occupied land; and (5) good discharged water quality. The municipal sewage treated by the method disclosed by the invention can reach a first-class standard A of 'pollutant discharge standards for urban sewage treatment plants'.