The invention discloses a flue gas denitration process for a CO exhaust-heat boiler of an FCC apparatus. Flue gas produced by an FCC regenerator is dedusted by a deduster, and before entering the CO exhaust-heat boiler, a cloud of flue gas is led out and used as a diluent gas for ammonia gas; and the flow of the diluent gas is 0.1 v%-5.0 v% of that of the original regeneration flue gas. The rest of the flue gas has energy recovered by a flue gas turbine, and is sent into the CO exhaust-heat boiler. The upper part of a high temperature evaporation section of the CO exhaust-heat boiler is provided with an ammonia injection grid, and an SCR denitration catalyst module is arranged between a low temperature evaporation segment and a high temperature economizer. The process provided by the invention uses FCC regeneration flue gas as the diluent gas for ammonia gas to dilute and carry the ammonia at the same time, so as to improve the mixing effect of ammonia gas and flue gas, not increase the rate of oxygen content rate of the CO exhaust-heat boiler, and avoid security risks; at the same time CO removal, waste heat recovery and denitrification of flue gas are accomplished in the CO exhaust-heat boiler, thereby omitting a separate SCR denitration reactor.