We report a spectrophotometic method for the determination of cyanogen chloride (CNCl) in air pollution.Experimental parameters for the stability and absorbility of CNCl gas in the different media were studied.The experimental conditions were optimized for CNCI as follows:absorbent:1%isonicotinic acid-barbituric acid;reaction acidity:pH 5.8 in phosphate buffer at room temperature;masking agent:0.01mol/L EDTA;λmax:598nm. The apparent molar absorptivity was found to be 1.17×105L·mol-1·cm-1,the linear range was within 0～5μg of CNCl in 25 mL solution; the regression equation of the curve has given by A=-0.0040+1.935C(r=0.9999).The method has been applied to the determination of CNCl in chimney gas,workshop air and production area air of the cyanuric trichloride plant,chemical works and pharmaceutical factory air.The relative standard deviation was below 2.7%(n=4)for the cyanogen chloride amount within 13～64mg/m3,and when CNCl amounts were within 0.1～1.0mg/m3,RSD was below 6.9%(n=6).The recovery was 98.7%.