A new approach using transient electromagnetic field signal for earth fault locating in non-solidly earthed overhead lines is presented. The characteristics of electromagnetic field in different directions under lines are analyzed in detail. Also， the product of vertical electric field after Hilbert transformation and horizontal magnetic field in SFB is determined the direction of the fault. The earth fault can be located in accordance with the difference of fault directions before and after fault. Some performance of the proposed method and the anti-interference measures adopted are introduced. Finally， experiment and simulation results verify the feasibility of this approach.