The invention discloses a modified electricity-larceny-prevention intelligent early-warning system and method, and belongs to the field of intelligent electric network informatization. The system comprises a data source module, a storage module, a diagnosis module and an early-warning module. According to the method, a large-data analysis model of the user electricity-larceny behavior probabilityis established, multi-dimension analysis is carried out, and suspected electricity-larceny users are accurately identified; the method is applied to electricity-larceny-prevention business, the bottlenecks that present manual electricity larceny prevention is large in monitoring workload, analysis workload and checking workload and low in accuracy are solved, and a reliable technical support is provided for primary electricity checking on the scene and electricity-larceny-prevention analysis and investigation work accurately and efficiently conducted by electricity-larceny-prevention workers.After configuration is set, manual interference is not required, the electricity-larceny behavior of an electrical power system is independently and accurately analyzed and early warned; the bottlenecks that present manual electricity larceny prevention is large in monitoring workload, analysis workload and checking workload and low in accuracy are solved, and the rationality and the accuracy of electricity net sources are improved.