The invention belongs to the technical field of direct current, particularly relates to a method for protecting direct current electric transmission line travelling wave. A protection detection deviceis arranged between the rectifier and an inverter filter near one side of a rectifier side, and a fault point is respectively arranged beside a line terminal and a smoothing reactor; according to fault voltage and current instantaneous values, change rates of a polar wave are calculated, polar wave sequence column vectors of n data values in data windows with the largest change rate are respectively collected and respectively denoted as Y and K; a row vector A containing n values is set to solve that A satisfies AY/AK as the biggest value under a nonlinear constraint condition; the data windows are moved to regain wave sequence column vectors, and the wave sequence column vectors are respectively denoted as Y1 and K1, a reference value delta satisfies that the delta is greater than the biggest value of Ak1 and less than the biggest value of AY1; according to real-time data of a travelling wave shape, a column vector P of a polar wave data value is calculated, if AP is greater than thedelta, it is thought that short-circuit fault happens in the line; if AP is less than or equal to the delta, it is thought that the short-circuit fault does not happen in the line.