Abstract: The existing problems in the method of formation austenite grain by heating in GB/T 6394-2002 “Metal Average Grain Size Determination Method” were analyzed from theoretical and practical aspects. And revision opinions were put forward at the same time, that is, to distinguish the grain size formed by heating and the grain size directly revealed by etching without any heat treatment, and the conception of “standard grain size” was put forward in order to distinguish the actual grain size.