The invention discloses an electricity usage trend abnormity suspicion analysis method and an anti-electric-larceny monitoring system. The method includes the steps of electricity usage information state estimation, electricity usage abnormity suspicion analysis of low-voltage public transformer platform regions, suspect user filtering and positioning and key suspect user monitoring, and an anti-electric-larceny knowledge base is involved in the method. The step of electricity usage information state estimation is used for dealing with abnormities and deficiency of electric energy collection readings, asymmetry of standing book information and other abnormities. The step of electricity usage abnormity suspicion analysis of the low-voltage public transformer platform regions is used for analyzing electricity usage abnormities of users in the low-voltage public transformer platform regions. The step of suspect user filtering and positioning is used for filtering out suspect electric quantity major users and positioning the suspect major users. The step of key suspect user monitoring is used for tracking electricity usage abnormity users. The anti-electric-larceny knowledge base is used for accumulating anti-electric-larceny basic knowledge. The method is used for achieving the ultimate purposes of automatically positioning the suspect users by analyzing the electricity usage abnormities of the users in the low-voltage public transformer platform regions, forming a checking name list, lowering the technical analysis intensity of anti-electric-larceny staff and improving analysis efficiency.