The standard HG/T 5666-2019 "Spinning & weaving dyeing and finishing aids, anti-coacervation leveling agents, determination of anti-coacervation effect" specifies a method for determining the anti-coacervation effect of anti-coacervation leveling agents in Spinning & weaving dyeing and finishing aids. This standard is suitable for evaluating the ability of anti-coacervation leveling agents to prevent coacervation phenomenon in the same bath dyeing process of disperse dyes, cation dyestuff and/or acid dyestuff. The standard describes in detail the experimental conditions and operating procedures to ensure the accuracy and repeatability of the determination results. In addition, the standard sets out the necessary terms and definitions, including the definition of anti-coacervation levelers and anti-coacervation effects, providing clear guidance for the understanding and application of the standard.