The invention provides a power transmission line parameter identification method and system. The method comprises the following steps: reading a double-ended wave recording file of a faulty line, andobtaining double-ended electrical quantity information of the faulty line; carrying out time synchronization on the double-ended electrical quantity information of the faulty line; and carrying out line parameter identification according to the synchronized double-ended electrical quantity information of the faulty line, so that a reactance identification value is obtained. By virtue of the technical scheme provided by the invention, power transmission line steady state parameter identification based on fault wave recording data is realized, and synchronization alignment treatment is carried out on the fault wave recording data, so that non-synchronous time of the double-ended wave recording file is shortened, a new means and a good data foundation are provided for accurately identifying power grid branch circuit parameters of a dispatching master station, power grid branch circuit steady state impedance parameter identification accuracy is practically improved, and further the accuracy and availability of a power grid online dispatching analysis software result are improved.