Abstract: A new application of multi-point method is presented in this paper, which is for the measurement of "cold test parameters", the reflection coefficients at the output termination and attenuator of helix Traveling Wave Tube (TWT). The measurement method of the reflection coefficient of the probe used in the measurement of "cold test parameters" is also discussed. The method is nondestructive and easy, and can also be used in other measurements of the reflection coefficients of device which has similar special structure.