With the increasing number of high-voltage transmission lines,most of the lines are installed in a non-transposition manner.The reason for the error caused by the single-phase power measurement method used for measuring the three-phase impedance parameters of single-circuit non-replacement lines is incorrect.Since the measurement circuit takes into account the influence of the earth resistance on the impedance parameters,Analyzed and proposed a new method for measuring earth resistance.When calculating the three-phase impedance parameters of a single-circuit non-commutation line,the calculation of the three-phase impedance parameters is brought about the large error by the inverse operation of the current matrix,and derived the expression of the error term,in order to reduce the error,the paper proposed the use of double-end measurement method to measure the voltage and current at the beginning and end of the three-phase line,and finally to a single 500kV single back does not change for the bit line,for example,the three-phase voltage and current obtained by the first and the end can reduce the error when calculating the three-phase impedance parameters of the single-circuit non-commutated line,and the feasibility of the method is verified.