The invention discloses an accuracy detection method based on an average power error for an analog input combining unit. The method is characterized in that the average power error is taken as the basis for judging the metering accuracy of the analog input combining unit, and an accuracy detection circuit of the analog input combining unit is constructed by a three-phase analog standard source with zero-crossing synchronous clock output, a three-phase standard electric energy meter and message analysis module equipment. During testing of the analog input combining unit, the three-phase analog standard source outputs three-phase symmetrical analog voltage and current signals, and the voltage and current power factors are adjustable; an output synchronous time tick clock is synchronous to a phase A voltage zero-crossing point, and the synchronization accuracy is 0.2us; the output voltage and current accuracies are 0.02 in grades; the format of an output synchronous time tick clock signal is consistent with the time tick clock format of he tested analog input combining unit, namely, both formats are IRIG_B code. Through adoption of the detection method, the average power error value of the analog input combining unit is directly provided through a detection result, and the metering performance of the analog input combining unit can be better embodied.