This standard specifies the water quality requirements for seawater chilled down water and uses the Spectrophotometric method, spectrophotometry method for the determination of zinc content in seawater chilled down water. It is suitable for seawater chilled down water with zinc content from 0.2 mg/L to 5.0 mg/L. By detailing the determination principle of zinc, reagent preparation and operation steps, this standard provides technical guidance for the monitoring of zinc content in seawater chilled down systems, which helps to avoid corrosion of equipment caused by excess zinc and improve the operation efficiency and safety of chilled down systems.