Natural-derived hydrogels are expected as promising structural biomaterials, but the soft character severely limits their applications. Here, a facile yet effective strategy was developed to fabricate super-strong and tough alginate composite hydrogels via a self-reinforcing method. The strategy was based on the incorporation of alginate materials with distinctive anisotropic features (fibers, fabrics and aerogels) into the precursor solution of congeneric hydrogels, followed by the in situ ionic-crosslinking. Interestingly, triggered by the concentration difference, the cations-Ca2+ in reinforcing phase could diffuse into the interface and simultaneously chelate with alginate chains of both reinforcing phase and hydrogel matrix, acting as self-generating interfacial binders. Contributed by the intimate interface, the load was effectively transferred into the rigid reinforcing phase, and the hydrogels integrated them into a mechanical network. This research offers a new path to design the interfac of polysaccharide composites without extra coupling agents.