Abstract: To solve the problem that the outer cylinder distribution parameters,joint connection parameters and other tests seriously affect the accuracy of value traceability in the process of testing communication cable transfer impedance using the tri-coaxial method in the field of high-precision measurement and calibration.By separately measuring the S parameters of the fixture calibrator and the cable under test,using the network cascade algorithm to calculate the shielding attenuation,and finally calculating the transfer impedance,the error can be effectively eliminated,aiming to improve the accuracy of the transfer impedance measurement.Starting from the measurement principle of the tri-coaxial method,the standard test plan is analyzed,the two-port S matrix and A matrix conversion and network cascade algorithm are discussed in detail,and an accurate measurement plan for transfer impedance is derived.It was verified through experiments and the Monte Carlo Method (MCM) was used to evaluate the measurement uncertainty,and the evaluation result was U_r=8%（k=2）.

Key words: Communication cables, Transfer impedance, Network, Cascade, Uncertainty, Monte Carlo Method(MCM)