Aiming to the problems of more difficulties on engineering implementation and more system complexity caused by data feedback of synchronous pulse method in IEC60044-8 standards, this paper proposes a solution to the data synchronization in merging unit based on piecewise linear interpolation method. First of all, a piecewise linear interpolation function is built to do error analysis based on remainder functions. Theoretical derivation, numerical analysis and experimental verification indicate that the piecewise linear interpolation algorithm has lower complexity , better synchronization and better sampling precision which excels the relative specification in state standard on transformer substation.