This paper studies the reconfiguration design and migration from an old path set to a new path set in multifiber wavelength-division-multiplexing networks. For the reconfiguration design phase, we introduce the functions of wavelength fragmentation cost and reconfiguration cost, and we propose a reconfiguration design that minimizes both wavelength fragmentation and the number of changed wavelengths. For the migration phase, we propose a migrating sequence algorithm that uses spare wavelengths to break the dependency cycle between before and after reconfiguration design sets and thus prevent service disruption. A numerical evaluation shows that the number of fibers is suppressed 4%–15% compared to the design without employing fragmentation cost and that the number of changed wavelengths is reduced by approximately 50%–90%.