The invention discloses a fault positioning method for an extra-high-voltage half-wavelength alternating-current transmission line. Through the method, fault positioning of a non-manually tuned extra-high-voltage half-wavelength alternating-current transmission line at 1,000kV or above under various fault types is realized. The method comprises the steps that the length l of the extra-high-voltagehalf-wavelength transmission line, impedance parameters per 100km of the extra-high-voltage half-wavelength transmission line and admittance parameters per 100km of the extra-high-voltage half-wavelength transmission line are acquired; a phase constant beta and an electromagnetic wave transmission velocity v of the extra-high-voltage half-wavelength transmission line are obtained through calculation; an action moment t<1> of a fault starting element of a protection device at the sending end of the extra-high-voltage half-wavelength transmission line is acquired; and the distance L betweena fault position and the sending end of the extra-high-voltage half-wavelength alternating-current transmission line is calculated, so that fault positioning is realized. Through the method, the faultposition of the non-manually tuned half-wavelength transmission line can be quickly calculated, and a guarantee is provided for safe and stable operation of the line.