When transmission line ground fault occurs, the magnetic field below the overhead line reflects the line fault information. Short-circuit current along the transmission line changes, the magnetic field below lines is different correspondingly, it means that changes on magnetic field below the transmission lines can fully reflect the changes in current. Distribution network is mostly single-ended power supply. Since distribution network is complexity and the accuracy is low, a new non-contact magnetic field measurement based method is provided to detect faulty line and locate fault for single phase to ground fault occurred in distribution network. The magnetoresistive sensors installed on the towers can non-contact measure the magnetic field, the fault line and point of failure are solved according to the magnetic field amplitude and phase. Magnetoresistive sensor measurement accuracy is high and it is low cost, the fault span can be determined between two towers. MATLAB is used to establish a line model, simulation result shows the feasibility of the theory. This work is supported by National Natural Science Foundation of China (No.6140312).