The invention discloses a time domain measurement method for impedance broadband characteristic of large-scale electric equipment in the field of measurement of the electric equipment. According to the technical scheme of the invention, head-end voltage wave and tail-end voltage wave of a lossless coaxial cable transmission line are obtained by calculating reflection coefficients of a head end and a tail end of the lossless coaxial cable transmission line and according to the conduction time of the voltage wave from the head end to the tail end of the lossless coaxial cable transmission line; discrete fourier transform is performed on the head-end voltage wave of the lossless coaxial cable transmission line, and meanwhile time shifting and fourier transform are performed on the tail-end voltage wave of the lossless coaxial cable transmission line, so that the values of the reflection coefficient of the tail end of the lossless coaxial cable transmission line at different frequencies are obtained, and finally an impedance value of tested equipment at different frequencies is obtained. According to the method, the broadband characteristic of the equipment under high voltage can be reflected; the method also has the advantages of wide frequency range and high measurement accuracy and has important academic significance and engineering application value.