GB/T 3681.2-2021 specifies solar radiation exposure test methods for plastics, including direct natural weathering (Method A) and filtered sunlight weathering through window glass (Method B), to evaluate changes in the properties of plastics after specified exposure periods. The standard defines test conditions, specimen preparation, and result assessment requirements. Key equipment includes radiometers, ultraviolet radiation meters, and other meteorological monitoring instruments, along with dedicated specimen racks and conditioning devices. Specimens are fixed at designated exposure sites, and environmental parameters such as solar radiation and ultraviolet radiation are continuously monitored. Changes in the appearance, mechanical properties, and optical properties of the plastics are periodically evaluated. This standard provides a unified technical basis for assessing the weather resistance and predicting the service life of plastics.