Abstract: The grain size of the five I－series rating graphs in the GB/T 6394－2017 standard spectrum was measured using the intercept method and the area method respectively, and the results were compared and analyzed. The results show that there were deviations in the grain size levels obtained using different measurement methods. When comparing with the results of the rectangular area method, the most reasonable result was obtained when using the horizontal and vertical measurement grid lines of the intercept method to count cut off points, with an accuracy within the range of 0.15. When measuring equiaxed grain size, using the intercept method was more convenient and efficient. It was recommended to use the horizontal and vertical measurement grid of the intercept method to measure grain size.