Abstract: A method based on Creedon’s laminar flow theory is got to predict MITL operating point changing, which is resulted from the so called electron re-trapping. The method gives exact numerical solutions for MITL total current, cathode current and voltage, i.e., operating point, behind the reflected front when forwards operating point and diode impedance are given. The result with the method is consistent with PIC simulation and could be used to estimate the maximum effective current, which is useful to generate X-ray for radiography, transmitted from MITL to under-matched diode.