In order to improve the disadvantages of traditional hydrogels such as low mechanical strength and lack of responsiveness, different types of nanoparticles or nanostructures are added into the hydrogel network through in situ polymerization, self-assembly techniques, and other strategies, giving hydrogels a variety of special properties, such as stimulation sensitivity, optical or electrical properties, and reversibility. With the development of nano materials and synthesis technology, nanocomposite hydrogels have shown great potential in drug delivery, tissue engineering, motion detection, and wastewater treatment, and have been extensively studied in recent years. This review comprehensively elucidates the state-of-the-art preparation strategies and underlying response mechanisms of diverse stimulus-responsive nanocomposite hydrogels, spanning temperature, pH, humidity, electrical, and light responses. It systematically dissects their applications in biomedicine, environmental remediation, flexible sensing, and composite phase change materials. Moreover, it delves into future prospects and challenges, emphasizing the need for continuous innovation to unlock their full potential in emerging fields and address existing limitations.