This guide will provide testing methods for impedance measurement of alternating current (AC) transmission line and calculating methods for the RLC (Resistance@ Inductance@ and Capacitance) distribution parameters of the tested line. It will also provide testing and calculating methods to obtain mutual inductance and coupling capacitance between double circuit lines on the same tower. This guide will outline the measuring instruments and the safety of the measurement. In addition@ it will include test procedures to obtain the open circuit and short circuit impedances of the tested line as well as the formulas to get the distributed parameters from impedance measurements. Purpose The accurate parameter of power transmission line is the basis of precise power flow calculations@ stability analysis@ protective settings@ and line fault location. Therefore@ it is necessary to develop a uniform standard to provide technical guidance for the accurate line parameter measurement of ac transmission lines.