Thermochromic hydrogel smart windows represent a significant breakthrough in the field of building energy conservation, offering a revolutionary solution for intelligent thermal environment management through their ability to dynamically regulate solar transmittance. This review systematically summarizes the thermoresponsive properties and technical bottlenecks of thermochromic hydrogels in smart window applications. A comprehensive analysis of the advantages and limitations of this class of material in terms of phase transition temperature, optical performance, stability, and response speed is provided, while the progresses made in optimizing their performance through various strategies are discussed. As a prospect, in the future, the development of thermochromic hydrogel smart windows must prioritize broad-temperature adaptability, cost-effectiveness, and multifunctional integration to address current challenges and facilitate their widespread adoption and scientific innovation in building energy conservation.