Abstract: A verification method of merging unit tester based on the principle of digital real-time micro-difference is studied,this method can output the continuous digital message of IEC 61850-9-2 protocol after the high-speed sampling of the analog signal through the FPGA system,also real-time superposition of digital error is completed by error model.The device realized by this method can be understood as a high-precision merging unit that can set any ratio and phase error values,thereby it can complete the error calibration of the merging unit tester.Through the real-time simulation and physical test of the error model,the accuracy and stability of the error data can meet the requirements of relevant technical specifications.The application of this result will help improve the traceability system of the national digital electric energy measurement,and is of great significance to comprehensively promote the construction of digital power metering system.