GB 5084-2005 is a water quality standard for farmland irrigation, which aims to ensure the mass safety of agricultural production and agricultural products. The standard sets limits for pH value, chemical oxygen demand, suspended solids, total mercury, total cadmium and other indicators according to different irrigation water sources and differences in crop types. These indicators are related to soil structure, crop growth and human health. The standard also specifies the collection, detection methods and Frequency of water samples. Meeting the standard water quality can not only meet the needs of crop growth, but also avoid soil pollution and harmful substances in agricultural products exceeding the standard, providing key guidelines for scientific and reasonable irrigation and sustainable agricultural development.