The quantization error of IEC61850-9-1/2 protocol in digital energy metering system was analyzed in this paper, and the mathematics expression of relative uncertainty of power caused by quantization was deduced. The power error of different voltage and current ratio was simulated, and the relative uncertainty was calculated, which are consistent with the theoretical results. The research have proved that compared to 9-1,power error caused by the quantization of 9-2 is more bigger . Based on the studies of quantization error of IEC61850-9-1/2 protocol, the related suggestions for the calibration of digital electric energy meter is put forward, which has some reference value to engineering application and theoretical research.