The invention discloses a treatment method for biological nitrogen removal of reinforced sewage, which comprises the following steps of: 1, feeding all or partial treated sewage and sludge refluxed from a secondary sedimentation tank into a reflux sludge denitrification unit together by adopting division point inflow; 2, feeding the outflow of the reflux sludge denitrification unit and the residual sewage to an anaerobic unit or an anoxic unit; 3, feeding the outflow of the anaerobic unit to the anoxic unit, and refluxing the mixed solution of an aerobic unit to the anoxic unit; 4, feeding the outflow of the anoxic unit to a transition unit; 5, feeding the outflow of the transition unit to the aerobic unit, and refluxing the mixed solution of the aerobic unit to the anoxic unit from the outflow end of the aerobic unit; and 6, feeding the outflow of the aerobic unit to the secondary sedimentation tank to perform sludge-water separation. The method can be operated in multiple modes of A-A2O, nitrogen removal AO, inverse AAO and the like and has high controllability, and a system has strong nitrogen removal capability. The method is suitable for upgrade and reform of newly built sewage treatment plants of towns lacking the land and the conventional sewage treatment plants.