As a link between the electronic transducer and the two device, the merging unit is responsible for providing a unified voltage and current data source for the substation.However, the sampling value in data sampling, processing and transmission links generated in large data, communication delay and packet loss and other issues will be on the merging unit interpolation processing effects, and ultimately affect the measurement of electric energy.Based on the above typical issues of merging unit of interpolation algorithm and the impact of electrical power measurement error is analyzed, and build the digital substation system can test the metering error of the simulation results were verified by experiments.The results show that the typical problems of interpolation on the merging unit and the measurement error of electric energy is a significant impact, and the use of different interpolation algorithms the results of different effects.This study provides a quantitative reference for the design and optimization of interpolation algorithm for merging unit in digital substation.