Localizer(LOC) mode design of the commercial aircraft is designed to deal with the big overshoot caused by the geometry limit when the aircraft captures the Localizer signal and turns to the runway centerline. A method in which Flight Management System(FMS) calculates the lateral deviation between the aircraft and the runway centerline, is used beyond the LOC selected course sector. The geometry limit is part of the capture maneuver criteria, and LOC selected course sector is also used as the LOC mode activate criteria in order to allow pre-maneuver in some Instrument Landing System(ILS) approach scenario. The simulation results show that the method in the paper can decrease the overshoot caused by geometry limit effectively.