GB/T 14636-2021 focuses on the detection of industrial circulating chilled down water and scale. It uses atomic absorption spectroscopy (AAS) to determine the content of calcium and mg in it. This standard is applicable to the determination of calcium and mg in industrial circulating chilled down water with a mass concentration of 0.1mg/L-200mg/L, and the determination of calcium and mg with a mass fraction of 0.1% -50% in scale. Detailed principles, equipment, reagents, Sample Handling and analysis steps provide a unified and reliable method for the accurate detection of calcium and mg in circulating chilled down water and scale in the industrial field, helping to ensure the mass concentration of industrial production water and the operation of equipment.