The invention discloses an AAO (Anaerobic-Anoxic-Oxic)-biological contact oxidation strengthened denitrification and dephosphorization device and a real-time control method of low C/N sewage treatment. The system is mainly composed of a raw water tank, an AAO reactor, an intermediate sedimentation tank, a biological contact oxidation tank, a settling zone, a discharged water tank, an online control box and a computer. The real-time control method is as follows: a DO sensor online collects concentrations of dissolved oxygen in grid cells of the biological contact oxidation tank, and the computer calculates and outputs the concentrations to control the nitrification process; a NH<4+> sensor, a NO<3-> sensor, a NO<2-> sensor and a TP sensor online collect the concentrations of ammonia nitrogen, nitrate, nitrite and total phosphorus in the discharged water tank, and the computer calculates and outputs according to the signals collected by the sensors to adjust the aeration amount, the reflux ratio of nitrifying liquid and water intake C/N. By adopting the online real-time control equipment, the system operation is optimized, the energy is saved, the consumption is reduced, the carbon source and the aeration amount are saved and the residual sludge is reduced.