In order to precisely evaluate the measurement errors of a digital energy meter, the relations of influence quantity errors and the combined error must be researched. Due to the complexity of the measurement model, it’s difficult to find the formula of combined error, therefore a Monte Carlo method was used. Through Monte Carlo simulation, the distribution characteristics of combined error and influence quantity errors have been obtained, and their relations have been validated. The conclusion can provide a reference for the accuracy gradation of a digital energy meter, as well as the influence quantity limit errors determination.