Moving neutralization boundary (MNB) is an important foundation to understand and improve IEF. However, there are obstacles in theoretical predictions of MNB on IPG strips due to the unknown local concentrations of carrier ampholytes on commercial IPG strips and the time-varying boundary velocities. We introduce a recursion approach to extend the current MNB theories into the space-time varying MNB system. The recursion approach emphasizes the localizability of physicochemical parameters in the discrete time intervals and local positions in Lagrangian coordinates, such as local concentrations of carrier ampholytes, local OH concentrations, local boundary velocities, local judgments, etc. The boundary-position recursion equation in a complete time sequence was presented to quantitatively predict the MNB position-time curves by distinguishing three kinds of titration cases according to NaOH concentrations in rehydration buffers. The theoretical position-time curves and local relative judgments of boundaries were satisfactorily validated by corresponding images of boundary migrations achieved from the IPG-MNB experiments with the some typical NaOH concentrations-bromophenol blue-rehydration buffers on pH 4-7 IPG strips. The results achieved herein have evident significances to the development of moving reaction boundary and IEF.