A novel and practical scheme for resolving the measurement difficulty in power frequency parameters of transmission lines in an intensive interference environment is proposed. The key technique is described. In the meantime， a new measuring method of mutual inductance of partial double-circuit lines is also proposed. Hardware and software designs and implementation of the measuring device using the above technique are dealt with. Field-test result shows that the proposed scheme is rational. The device implemented can overcome the influence of intensive interference voltage on the measurement of transmission line power frequency parameters and meet practical engineering requirements.