The invention provides a low voltage network electricity theft detection method based on the AMI data. The method comprises steps that a phase voltage corresponding to a common point is calculated, and whether a user of a phase corresponding to the common point has electricity theft behaviors is determined. According to the method, an intelligent meter is utilized to measure the data, in combination with a low voltage network topology structure and line parameters, the user position of the three-phase low voltage network having bypass electricity theft behaviors and electricity theft time segments can be effectively detected, electricity theft quantity is estimated, and thereby an electricity theft problem is solved with pertinency .