Based on the decoupling of the jointed four transmission lines， a fault location algorithm is proposed. When the fault occurs in the jointed four transmission lines， the faulted phase electrical measurements can be decomposed into twelve-sequence component， which can be used to implement fault location. There is inverted sequence component under any faulted condition， the fault location method based on the inverted sequence component is proposed. When a fault occurs in the jointed four transmission lines， in the inverted sequence component networks， voltages calculated from two sides of lines are equal at the faulted point. Because twelve-sequence component method can decouple the mutual electromagnetic effect between lines， the accuracy of the fault location is high. A large number of EMTP simulations indicate that the algorithm is completely suitable for the jointed four transmission lines and the accuracy is not affected by the factors such as faulted resistance， generation mode and power angle， etc.