Favorable hydrogels can be used as a material to deliver bioactive molecules and improve the stability of bioactive substances, while their safety needs to be improved. In this study, protocatechuic acid (PCA) and Fe were rapidly self-assembled to form a metal-phenolic network under different pH conditions, and then sodium alginate (SA) was added to prepare the SA/PCA/Fe hydrogel without adding other chemical reagents. The structural characteristic of SA/PCA/Fe hydrogel was characterized by infrared spectroscopy, X-ray diffraction analysis and scanning electron microscopy. The results showed that the structures of SA/PCA/Fe hydrogels prepared at different pH values were significantly different. The texture analysis, water-holding measurement and rheological analysis indicated that the SA/PCA/Fe hydrogel showed higher gel strength, water holding capacity and storage modulus. Thermogravimetric analysis illuminated that the SA/PCA/Fe hydrogel enhanced the thermal stability of free anthocyanins through encapsulating anthocyanins. Moreover, in vitro simulated digestion experiment revealed that SA/PCA/Fe hydrogel could control the release of anthocyanins in the simulated gastrointestinal tract. To sum up, this present study might provide a safer and feasible way for the delivery of bioactive substances.