Electronic transformer is an important process-level device of the smart substation; it is responsible for collecting voltage and current information of the power system and transmits it to the process layer network for measuring, protection and control devices. As the digital interface between electronic transformer and process layer network, merging units plays an important role in electronic transformer error adjustment. Modifying the merging units internal scale factor to adjust the error value of electronic transformer is an important means to adduce the error value on-spot adjustment and ensure the accuracy.