Transient pulses generated by partial discharge have significant attenuation and distortion during transmission through the cable. Therefore, acquired pulses are difficult to reflect the original insulation degradation. In addition, reflectometry locates and evaluates faults based on reflected signals originating from defects. Accurate knowledge of the transmission characteristics of the cable can greatly guarantee the accuracy of these fault detection techniques, which require an exact simulation of the channel to reconstruct the signals transmitted through the cable to reach their origin without attenuation and distortion, where the propagation speed and attenuation of the signal are required. In this paper, we propose a method for extracting the high-frequency transmission characteristics based on scattering parameter measurements, which can Reject the dependence on the structural and material parameters of the cable and apply to scenarios where the cable is not perfectly symmetrical at both ends. The experimental results show that the proposed method can improve the measurement accuracy of the traditional method, especially in the characteristic impedance. In addition, the signal transmission in the cable can be accurately modeled by the estimated characteristic parameters.