Abstract For the high luminosity operation of the KEKB-factory, the beam injection time from the linac to the storage rings is desired to be short. However, the injection is sometimes interrupted by a temporary rf-trip of the klystron. In case of a serious failure, the klystron is switched to a spare one to compensate for the acceleration energy. After the switching, the injection is often degraded because of the beam optical mis-matching due to the change in the beam energy at each quadrupole. We have developed software which can estimate the beam energy at each quadrupole, calculate the optics so as to achieve the desired matching and change the settings of the relevant quadrupoles in short time. The experimental result of the recovery of the optical matching is also shown
