Effects of impedance discontinuity in magnetically insulated transmission line(MITL) region and diode time-dependent impedance on diode wave process have been studied through theoretical analysis. If the time delay of the transmission lines in MITL region is much shorter than the pulse width of the incident wave, the amplitudes of cathode voltage and current can be represented by those measured in the anterior part of the diode and the ratio of voltage and current is diode impedance. To steepen the leading edge of cathode voltage and current, the impedance of the transmission lines in MITL region is suggested to increase along the direction of the incident wave and should be the root-mean-square of the effective impedances on both ends. The leading edge of measured voltage and current can