The invention discloses a method for calculating a parameter of an electric power line, which comprises the steps of S1, sampling data measured by a synchronous phasor measurement unit, and acquiring sampling data; S2, solving an optimization problem with constraint conditions for the sampling data, and acquiring a parameter value of a line to be judged; and S3, judging whether the parameter value of the line to be judged conforms to preset conditions or not, if so, using the parameter value of the line to be judged as a final line parameter value; and if not, removing bad data, which does not conform to the preset conditions, in the sampling data, returning back to the step S2 to continuously solve the sampling data in which the bad data is removed. By adopting the embodiment of the invention, an impedance parameter of the electric power line can be calculated accurately, and the accuracy and the reliability of the acquired electric power line parameter are enabled to be greatly improved.