Abstract: When we use the transmission function or the electromagnetic analytic software to analyze the expandable measuring instruments transmission channel distributed parameter model, a certain amount of errors will occur. This paper presents a method to analyze the channel transient and frequency response based on finite difference time domain(FDTD) method and Baum-Liu-Tesche (BLT) equation. For the transient response analysis, an improved FDTD method is presented to analyze transient response in any location of channel with arbitrary terminal loads. For the frequency response analysis, the BLT equation is coupled with the thoughts of electromagnetic topology to analyze the frequency response in the node of transmission channel. Furthermore, the channel transient and frequency response are compared with the experimental measurement, and the test results are consistent with the theoretical results in the frequency range. It shows that in the channel working frequency range, the theoretical analysis is feasible for channel transient and frequency response analysis and thus can provide guidance for design of the matching circuit and improve the accuracy of transmission scheme.