With analyzing the performance of the existing one-ended protection and the effect of zero-sequence mutual inductance on ground distance relay， on the basis of the existing hardware configuration， a new one-ended mutual speed-up protection is implemented. It includes several improved elements. Dynamic simulation results show that the new protection can reliably and quickly operate under all kinds of in-zone cross-line and single-circuit line faults except when the in-phase overhead line fault happens at the outlet of the bus.