With the continuous appearance and expansion of high-strength hydrogels in emerging fields such as industry, medicine, and green development, the synthesis and application of high-strength hydrogels have developed dramatically and achieved remarkable results from the aspects of raw materials, preparation methods, and reinforcement mechanisms. However, there is still a lack of systematic reviews on high-strength hydrogels. Herein, we first discuss the advantages of natural and synthetic materials, and the characteristics of high-strength hydrogels prepared from different raw materials; we then expound on the influence mechanism of physical interactions or chemical bonds on the strength of the hydrogel from three aspects: physical cross-linking, chemical cross-linking, and dynamic chemical cross-linking; at last, we systematically expound the strengthening strategies, including double network/multi-network, nanocomposite, topology, supramolecular polymerization, and characteristics and strengthening mechanisms of such high-strength hydrogels. In addition, based on the development status of high-strength hydrogels, we combined the application requirements and the existing drawbacks of high-strength hydrogels to propose their possible development directions in the future.