The measurement abnormality on the power supply side is one of the important reasons that the line loss rate is negative. Taking into account the reasons for abnormal measurement is large, it is very difficult to find out the reason by on-site inspection method. In order to overcome this problem, the identification method of metering anomaly based on negative line loss analysis is proposed. In order to ensure the objectivity and comprehensiveness of analysis, the transformer and its secondary circuit, watt-hour meter, etc. are analyzed in detail according to the actual operation and national standards. And the main cause of negative line loss is extracted. In order to improve the efficiency of on-site inspection, the relationship between line loss rate before and after the measurement anomaly is deduced. Based on the data analysis and fault pre-assessment, a metrological identification method is proposed to analyze the possible anomalies and improve the on-site inspection accuracy. Finally, a numerical example is presented to verify the validity of the method.