GB/T 11905-1989 stipulates a method for the determination of calcium and mg content in water quality by Atomic absirption spectropho-tometry, AAS. It is based on the absorption principle of calcium and mg elements for specific wavelengths of light. The standard specifies the required equipment and requires the performance of the atomic absorption spectrophotometer. Detail the collection, storage and pretreatment steps of water samples to avoid interference with calcium and mg content. Standardize the test process, covering instrument debugging, standard Linear dispersion drawing and water sample determination. Through this standard, the calcium and mg content in water can be accurately determined, providing important data support for water quality analysis, water treatment process optimization, etc., and helping to ensure water mass.