The invention discloses an improved SNCR (selective non-catalytic reduction) denitration device for a CO incinerator and a denitration method. The improved SNCR denitration device comprises a liquid ammonia storage tank, an evaporator, a buffer tank, a mixer and an injection mechanism which are in series connection. The injection mechanism is connected with the CO incinerator, a bypass air inlet pipe and a blast pipe are connected to the mixer, the ejection mechanism comprises a first injection gun and a second injection gun, and the first injection gun and the second injection gun are positioned at the top and the bottom of the CO incinerator respectively. A plurality of third injection guns are arranged in the middle of the CO incinerator and staggered on two sides of the CO incinerator, and a partition plate is arranged between every two adjacent injection guns. A filter water tank is connected with a smoke outlet at the top of the CO incinerator and further connected to the CO incinerator through a bypass backflow pipe, and a joint of the bypass backflow pipe and the CO incinerator is positioned between the first injection gun at the top position and the second injection gun. The invention further provides an SNCR denitration method. By the improved SNCR denitration device and the SNCR denitration method, defects in the prior art can be overcome, and low-temperature efficient operation of the SNCR denitration device is realized.