As a key device of digital power metering system, The error of digital watt-hour meter directly determines the accuracy of the digital power metering system, digital watt-hour meter in signal input form have a lot of differences with traditional watt-hour meter, the input signal of traditional watt-hour meter is three-phase analog voltage/current and digital watt-hour meter is data frame that follow the IEC61850 protocol standard, so relative to traditional watt-hour meter the digital watt-hour meter have an important error source - frame loss error.In this paper analyzed theoretically the frame loss error of digital watt-hour meter, and derived the maximum allowed frame loss rate to digital watt-hour meter that determined level, at last, through experiment and simulation verification found that the frame loss error of digital watt-hour meter change with the number of lost frame, and the maximum loss error has nothing to do with the sampling frequency. Concluded that to ignore the digital power metering system loss error, digital watt-hour meter maximum allowable frame loss rate should below 5% of accuracy level, and it has a important significance to set up relevant surveillance project for digital watt-hour meter.