GB/T 2401-2025 "Cationic Dyes—Determination of Fibre Saturation Value, Dye Saturation Value and Saturation Factor in Acrylic Fibre Dyeing" has undergone technical upgrades based on the 2006 edition. As a key technical standard in the textile printing and dyeing industry, it clarifies the definitions and determination methods of fibre saturation value, dye saturation value, and saturation factor. Using specific reference dyes as benchmarks, the standard optimizes dyeing process parameters, extends dyeing time to 60 minutes, refines dyeing depth intervals, and employs stepwise calculation formulas to enhance testing accuracy. It also specifies requirements for reagents, materials, instruments, equipment, and operational procedures. This standard applies to the determination of relevant saturation characteristics when cationic dyes are used for acrylic fibre dyeing, providing scientific data support for evaluating dye-fibre compatibility and optimizing dyeing formulations.