Abstract: The stability for hardness testing results of HRB gauge and HRC gauge of the Rockwell hardness tester was studied by the mathematical statistics method. The results show that:the HRC gauge of the Rockwell hardness tester was stable and the values were reliable, and the HRC gauge could meet the needs of the daily testing requirements for imported and exported metal materials, but the stability of the HRB gauge was relatively worse. It was suggested that for the laboratories with busy testing work, it was better to test the HRC hardness and HRB hardness respectively with two hardness tests, or increase the frequency of intermediate check and calibration in order to insure the stability of hardness tests.