The invention discloses an electric transmission line single-terminal ranging method with the sudden change of current as the polarizing quantity. The method comprises the following steps that a current value and a voltage value at the protection installation position of an electric transmission line are obtained and are subjected to low-pass filtering, and a current fundamental component and a voltage fundamental component with high-frequency components eliminated are obtained; the current fundamental component and the voltage fundamental component after low-pass filtering are subjected to Fourier transform, then the current value, the voltage value and the compensation voltage value are computed, and the fault distance of the electric transmission line is measured by judging whether the compensation voltage value is the same as the phase position of the sudden change of current. The electric transmission line single-terminal ranging method is not affected by load current and fault types, the ranging precision is obviously superior to that of an existing single-terminal ranging method, the offside data of the line are not needed, synchronization is not needed, new sampling values are not needed, and the calculation amount is small.