Abstract: A time-domain segmented calibration method for a characteristic impedance of a time-domain reflectometer is provided. The method first segments the measured characteristic impedance value according to the reflection coefficients ?, determines several boundary points with the reflection coefficients, and divides the range of the measured impedance according to the impedance values corresponding to the reflection coefficients of the boundary points, and then select a typical impedance value in the range as a reference impedance for calibration. The TDR instrument performs characteristic impedance calibration for each typical reference impedance value one by one, and stores them as calibration parameters of different groups. With respect to different impedance value ranges, the selection ranges of the calibration and measurement areas of TDR are different. When the measurement is performed, the 50? calibration parameter is used as the default reference for calculation.