A single-ended fault location algorithm is proposed, based on the improved distributed-parameter method and variable time windows of traveling wave. According to the online estimation of the opposite terminal source impedance, the improved distributed-parameter method can be built, to enhance the location-error distribution regularity and improve the feasibility of the assembled fault location algorithm. Then based on the study of the location-error distribution of the proposed improved distributed-parameter method, the variable fault distance window can be computed, determining the variable time windows of the reflected waves to be identified. At last, considering the wiring schemes of local and opposite buses combined with the impact of the interference waves from adjacent buses, reflected waves contained in the variable time windows can be identified and the exact fault location can be detected. Simulation results demonstrate the high reliability and accuracy as well as the engineering application value of the proposed algorithm.