Abstract: It is not practical for the RGH currently carried out to be regarded as a fixed variable (including JJG168-87 Standard). Based on the analysis of the vertical tank structure, those RGHs. collected home and abroad proves to be variables. Because the randomness of RGH exists in the capacity calibrating and measuring of vertical tank, the calibrating and measuring accuracies will be significantly influenced, so, the RGH even exceeds its allowable tolerence in many cases. Meanwhile, the paper points out that the current "stable RGH "is still inaccurate, so more attention had to be paid to the current measuring method in this case. A revising method has been given by the author in the paper.