A fluctuation belt ecological slope protection system that responds to hydrological variation includes a runoff treatment system and an ecological floating island system. The runoff treatment system includes a grass planting side ditch and a water accumulation pit-pond. The ecological floating island system includes an ecological floating island and an ecological gabion base. The ecological floating island includes a flexible substrate, and aquatic plants. The ecological gabion base is positioned below the ecological floating island. The ecological protection system is suitable for a fluctuation belt and consists of a runoff treatment system and a separable ecological floating island system. Rain water on bank slope is purified and collected as wet soil is stabilized, the protection system responds to backwater water level variation in fluctuation belt, providing growing space for plants, organisms, and fish, following variation in water level, enriching the ecological environment of the fluctuation belt, and improving scenic effect.