The DB34/T 3689-2020 standard specifies the determination of the content of five isothiazolinone biocides in water-based paints, which are analyzed by High performance liquid chroma-tography, HPLC (HPLC). Iothiazolinone biocides are widely used in Coatings as preservatives to prevent microbial growth. The standard details the operation procedures, instrument requirements, Sample Handling and test conditions of High performance liquid chroma-tography, HPLC to ensure the accuracy and Reliability of the determination results. Through this method, the content of harmful substances in water-based paints can be effectively monitored, the safety and environmental friendliness of the products can be guaranteed, and the requirements of relevant regulations can be met to promote the healthy development of water-based paints.