The invention discloses a method for measuring phase self-admittance and phase self-impedance parameters of alternating-current extra-high voltage same-tower double-circuit lines. The phase self-admittance measurement method includes the following steps that (1) the head end and the tail end of a phase to be measured are in an open state, and the head ends and the tail ends of other phases not to be measured are short-circuited over the ground; (2) alternating-current voltage is applied to the head end of the phase to be measured, the head end and the tail end of the phase are synchronously measured to obtain head end voltage, head end currents, tail end voltage and tail end currents of the phase to be measured, and the time error of synchronous measurement of the head end and the tail end of the phase to be measured is smaller than 1 microsecond; (3) self-admittance is obtained according to a formula. A traditional measurement method is changed, distribution parameter characteristics of a wiring mode and an algorithm, influences of other phases on the phase to be measured and existence of power frequency interference are considered, especially in a long-distance electric transmission and distribution circuit, errors of self parameters measured in the method are reduced and requirements of a project are met.