With the wide use of analog merging units in smart grids, the market is in urgent need of a convenient and quick merging unit test tool. Firstly, the paper analyzes the shortcomings of the analog merging unit tester in the present market. Then, it carries out the overall design, hardware design and software design of the analog merging unit tester. Finally, the test device is tested and verified. It proves that the tester designed in this paper has automatic test function, which enhances the detection efficiency and shortens the test period, and also can improve the reliability of the test and the accuracy of the record of the test results.