The invention provides a method for enhancing biological denitrification and denitrification of low-temperature sewage in winter. The method comprises the following steps: reacting acclimatized activated sludge and nitrate wastewater in four continuous stirring reactors in an operation mode of a sequencing batch activated sludge process, and controlling the temperature of water in the reactors at 5-15 DEG C by using a cooling water circulator; taking samples from the four reactors, and determining the total nitrogen, wherein the maximum discharge standard for total nitrogen in national GB18918-2002 is 20 mg/L; and analyzing whether the finally discharged total nitrogen amount reaches the standard according to the detection result. The method can obviously enhance biological denitrification after adding a mediator at low temperature, and satisfies the maximum discharge standard for total nitrogen in Chinese Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002). The application of the redox mediator overcomes the defect of low biological denitrification rate at low temperature, and provides a new idea for high-efficiency degradation of nitrogenous pollutants.