The ISO TR 22770 standard provides a Colorimetry-based technical support for the analysis of steel surface preparation grades before painting. This method uses Colorimetric analysis combined with visual evaluation to quantify the color change of steel surface preparation, helping to judge surface preparation grades more accurately. The standard describes in detail the equipment, test procedures and data analysis methods of Colorimetric measurement, aiming to improve the objectivity and conformity of surface preparation grade evaluation. This method is suitable for surface cleanliness and asperity evaluation of steel before painting, providing a scientific basis for painting quality control, especially in industrial corrosion protection and high-demand painting scenes.