The invention discloses a weighted least square algorithm-based ultra-high voltage transmission line fault positioning method. The method includes the steps of: establishing an ultra-high voltage transmission line distributed parameter model: according to distributed parameter characteristics of a transmission line, cascading and superposing voltage and current on infinite small segments of the transmission line to obtain the distributed parameter model; processing parameters in the ultra-high voltage line according to the established model, i.e., simplifying wave impedance Zc and a propagation coefficient r; calculating positive sequence, negative sequence and zero sequence voltage of a fault point according to sending end measured values, and calculating positive sequence, negative sequence and zero sequence voltage of the fault point according to receiving end measured values; introducing phase angle displacement delta to represent a displacement phase angle of the sending end lagging behind the receiving end, adopting a weighting method to allocate proportions of unmatched voltage components of the zero sequence, positive sequence and negative sequence, and determining a fault position based on the weighted least square algorithm. The method provided by the invention establishes the distributed parameter model of the ultra-high voltage transmission line, and reduces a model error caused by simple processing of a lumped parameter model adopted by a short line.