The bus will experience different voltage sag when fault occurs at different location. Based on the non-liner profile characteristic of voltage sag measured at the bus, the paper proposes a new fault location method. Firstly, it obtains the analytical expression of each section based on the relationship between voltage sag and fault location. Then calculate the fault distance using chord secant method and identify the faulted section through the minimal deviation of fault distance. The combined two results of fault distance and faulted section make fault location accurately. It overcomes the difficulty of radial power distribution systems fault location. Through simulating for the IEEE 13 node test feeder with different faults, including various fault resistance, loading variation and the connected distributed generation, it proves the method’s accuracy and effectiveness.