The invention belongs to a synchronous line loss anomaly analysis method, and particularly relates to a synchronous line loss comparative analysis method based on theoretical line loss calculation. Apower transmission network is analyzed through an ETL assembly, a power distribution network model is automatically updated and automatically matched with a same-period system, and theoretical partialpressure, power transmission line loss, wiring loss and transformer area loss are generated through combination of a partial pressure calculation relation automatic generation technology based on electric quantity classification expansion and theoretical calculation. On the basis of combination of gateway automatic matching and manual matching, comparative analysis with the line loss in the sameperiod is realized. By means of the technology, the conditions that the number of abnormal reasons of the synchronous line loss system is large, and the troubleshooting process is complex are improved. The multi-dimensional difference analysis method for comparing the same-period line loss result with the theoretical line loss result assists the same-period line loss system in quickly positioningthe cause of the abnormal line loss, and lays a foundation for loss reduction potential analysis.