The invention relates to a device and method utilizing a colorimetric method to measure the 
ammonia content of 
flue gas. The device comprises a 
flue gas sampling temperate constant device, a 
flue gas absorbing and acidifying device, a 
flue gas liquefying and absorbing device, an absorption liquid metering device, a precise 
time sharing addition device, an absorption liquid mixing and color-developing device, and an absorption liquid colorimetric device. The provided method comprises the following steps: 
processing the 
ammonia in 
flue gas, transferring the 
ammonia from the gas state to the 
liquid state, precisely quantifying the absorption liquid, adding precisely quantified chemical reagents, developing the color in the absorption liquid colorimetric device, measuring the 
absorbance of color developed liquid, and finally calculating the ammonia content of 
flue gas according to the 
absorbance of color developed liquid. According to the method, the ammonia in flue gas is transferred to a liquid solution, and 
crystallization and adhesion of 
ammonia gas are avoided. The colorimetric principle is utilized, the concentration of 
ammonium salt in absorption liquid is measured and can be converted into the concentration of escaped ammonia in flue gas, and thus the precise measurement is achieved.