This article analyzes the energy efficiency evaluation indicators of data centers and highlights the importance of accurate measurement of electrical energy data. Based on the characteristics of online operation of power meters in data centers, a practical method for online instrument calibration and comparison is proposed. This method allows standard meters to be installed in parallel with the meters under test on the same circuit, without disrupting the normal operation of energy-consuming equipment. The timing start condition is based on the change in the last digit of the tested instrument, and the timing stop condition is based on the change in the last digit, which improves the accuracy of synchronous timing. Two practical error discrimination methods are proposed for the measurement comparison results. For instruments with large errors that cannot participate in energy efficiency calculations, a proportional correction method is adopted, and a correction coefficient is introduced. Considering the large number of meters in data centers, sampling principles were proposed, and the effectiveness of the method was verified through engineering empirical analysis.