Abstract: The grain size assessment of GH4169 nickel based high-temperature alloy was carried out using comparative and intercept methods, and the influence of different corrosion methods, inspectors, and assessment methods on the material grain size assessment results was analyzed. The results show that different corrosion methods had a significant impact on the grain boundary display effect of materials. When the material underwent chemical corrosion or electrolytic corrosion, and the grain display effect was poor and could not meet the evaluation requirements, the hot acid corrosion method could be used. When the uniformity of material grain structure was poor, there was a significant difference in the results of evaluating grain size using comparative method. For samples with uniform grain structure and good grain boundary contrast, the difference in grain size assessment results among different inspectors should be at least 0.5 levels. The accuracy of using the intercept method to evaluate grain size was relatively high, and its uncertainty mainly came from intercept statistics, but the uncertainty introduced by this statistical process was usually less than 0.1 level.