This product adopts isonicotinic acid-barbituric acid spectrophotometry, according to the fact that cyanide and chloramine-T can generate cyanogen chloride under the action of active chlorine, and then react with an isonicotinic acid-barbituric acid reagent to generate violet blue The degree of the colour change of the solution is proportional to the concentration of cyanide in the water, and the concentration of cyanide can be obtained according to the color photometric detection of the color.