The results on the use of time-domain reflectometry (TDR) for studying the dynamic impedance of the magnetically isolated coaxial diode (MICD) are presented. The experiments on exact binding of high-current beam emission to the front of the accelerating pulse are carried out with emitting edge radius variation of the tubular cathode, and also in the dependence of the dispersion of used graphite. The features of the MICD impedance dynamics in different magnetic fields are stated.