Abstract: The testing principles of dual extensometer and strain gauge coaxiality testers were analyzed, and the sources of measurement uncertainty for the two testing machines were analyzed. The degree of influence of different factors on the measurement uncertainty of the two testing machines were study. The results show that when using a dual extensometer coaxiality tester, more attention should be paid to factors such as the accuracy of the extensometer, the alignment of the fixture and the uniformity of the material. When using a strain gauge coaxiality tester, additional factors such as the position of the multi section patch, linear errors in the data acquisition system, and positioning deviations during each reinstallation should be considered. The dual extensometer coaxiality tester was suitable for routine coaxiality calibration of testing machines. The strain gauge coaxiality tester was suitable for coaxiality testing that required high accuracy and comprehensive analysis.