The traditional parameter measurement methods of T-connection transmission lines are based on the symmetry of three-phase parameters of the lines, without considering the influence of the asymmetry of three-phase lines on the parameter measurement. The existing parameter measurement methods of asymmetrical transmission lines are not applicable to the T-connection transmission lines. A parameter measurement method of three-phase asymmetrical T-connection transmission lines is proposed. The Levenberg-Marquardt (L-M) optimization algorithm is applied to solve the parameters of the nonlinear parameter equations of the transmission lines. The feasibility of using the L-M algorithm to calculate the parameters of the system of nonlinear equations is verified by the simulation of parameter measurement method of the asymmetrical single-circuit line in PSCAD. Then, the parameter measurement method of the asymmetrical T-connection transmission lines proposed is simulated, which proves that the parameter measurement method of the asymmetrical T-type transmission line is correct and feasible. This work is supported bySpecialized Research Fund for Doctoral Program of Higher Education (No. 20110141110032).