The invention discloses an electric line fault alternating-current impedance fast tracking and judging method. The method relates to a high voltage alternating-current detection power supply (1), a current detection unit (2), a voltage detection unit (3) and a line sensor (4). After an electric line is tripped due to a fault, high-voltage alternating-current detection signals are sequentially applied to the phase-to-ground and the interphase of the line through the line sensor installed on the outer side of a line switch, and phase-to-ground impedances Za0, Zb0 and Zc0 and interphase impedances ZAb, Zbc and ZAc of the line fault are calculated. The detection result is compared with the lowest operation criterions Za0j, Zb0j, Zc0j, ZAbj, Zbcj and ZAcj, whether the line fault is an instant fault or a permanent fault is tracked and judged, and the fault recovery is conducted. The electric line fault alternating-current impedance fast tracking and judging method is fast in speed, accurate in judgment, suitable for a line grounded short circuit and an interphase short circuit, thereby having the better practicability.