The "DB37/T 4156-2020 Water Quality, Determination of Actinomycetes Spreader Plate Method" standard stipulates the method and technical requirements for the determination of actinomycetes in water by Spreader Plate Method, including the scope of application, reagents and equipment, sample collection and treatment, operation steps, result calculation and reporting. This standard is applicable to the detection of actinomycetes in surface water, groundwater and industrial and domestic wastewater. The accuracy and repeatability of test results are ensured by clarifying the detection process and quality control requirements. The standard provides technical guidance for the monitoring of actinomycetes in water quality, and provides an important reference for environment protection, water quality management and related research.