The invention relaxes to a replacement scheduling method and system for ultra-low loss optical fibers in a backbone network, which are designed to improve spectrum, utilization efficiency. The method includes: S1: calculating a gam respectively after each optical fiber link is replaced, that is, calculating a product of multiplying a quantity of frequency slots (FSs) reduced after each optical fiber link is replaced by a remaining time for finishing replacing all the remaining optical fiber links; S2: selecting an optical fiber link having the highest gain after the optical fiber link is replaced to perform replacement; and repeating S1 and S2 until all the optical fiber links that need to be replaced have been replaced. In the present invention, a replacement order of optical fibers is arranged most appropriately, so as to save as many as spectrum resources for operators for use by additional services. (FIG. 2)