Based on an in-depth analysis of the working mechanism and operation of the current three-phase Watt-hour meter, the paper points out the design defects of the three-phase Watt-hour meter, analyzes the typical cases and proposes the improvement measures. Through analyzing and testing, when there is three-phase reverse active electricity, it is found that the current three-phase Watt-hour meter has measurement defects on distributed generation Internet connection, wrong wiring, line loss calculation and other aspects, and that it cannot accurately measure the actual forward and backward electricity, resulting in settlement errors, wrong electricity amount and inaccurate line loss, etc. This paper is of great significance to the accuracy of measurement and settlement and the improvement of the function of Watt-hour meter.