The invention relates to a method for reducing the generation of a nitric oxide of a thermal power generating unit. After being subjected to electrostatic precipitation and cleaning, flue gas is fed in a primary air system through a recirculating pipeline, and is used as pulverizing system carrier air to enter a hearth, so that the oxygen quantity of the in-furnace combustion area is effectively reduced, the overall oxygen quantity and temperature of the lower part of the hearth are beneficially reduced, the secondary combustion-supporting air action effect is beneficially improved, and the generation of the nitric oxide can be reduced; meanwhile, the heat absorption capacity ratio of in-furnace radiation heating and heat convection are changed, and the hearth temperature is reduced alongwith the increase of the recirculating flue gas amount, so that the radiation heat absorption capacity is reduced, but the flue gas temperature of an outlet of the hearth has a little change, and theheat adsorption capacity of a convection heating surface is increased along with the increase of the flue gas amount, so that the purpose of increasing the reheat steam temperature is achieved.