The invention provides a low-voltage distribution line fault detection method and system. The method comprises the steps of: obtaining fault information sent by a low-voltage power utilization acquisition device; and establishing a topological structure model of a power distribution and utilization device according to acquired network nodes of the power distribution and utilization device and thegeographical position information of the power distribution and utilization device, taking the low-voltage power utilization acquisition device to which the fault information belongs as an originatingpoint, and searching and determining the fault position according to the topological structure model. According to the method, low-voltage fault pre-judgment and rapid and accurate positioning of thefault position and the power failure range are achieved, and the field work force is arranged according to the accident processing priority, so that resource waste caused by repeated and wrong use ofrush-repair vehicles is avoided, the power failure time is shortened, and the emergency rush-repair management level of a power distribution network is improved.