Abstract: At present, the energy requirements of the world mainly depend on fossil fuels, thus inducing a series of issues, and the energy reserves do not meet the people's increasing demand. Therefore, using energy efficiently becomes more and more important. While the global contribution of buildings to final energy consumption accounts for 20%-40%, reducing the energy consumption of building is an efficient way to cut the total energy consumption. Windows are often considered as the least insulating building component with a huge maintenance requirement and therefore a key part for economizing energy uses in buildings. Smart window system is a typical example for economizing energy uses in buildings. It can be designed to control the amount of transmitted heat and light under the application of electricity (electrochromism), light (photochromic) or heat (thermochromic). Among them, thermochromic materials have attracted much attention because they can be used with zero-energy input and solar energy itself is utilized as a booster against solar heat. Thermochromic hydrogels, as one of the best thermochromic materials for smart window, have attracted much attention. It refers to polymers exhibit reversible changed phase morphology with variation of temperature, which leads to an optical shift between opaque and transparent. For example, when the outdoor temperature is lower than the critical temperature, smart window based on the thermochromic materials remains a transparent state, and solar transmission is increased to capture free heat from the sun. If, however, the indoor temperature increases higher than the critical temperature of smart window, it will become opaque to reflect or block the transmission of solar light to reduce power consumption. In this paper, the latest progresses on application of thermochromic hydrogels as novel materials of energy chemical engineering in smart window are summarized, and the possible development directions of thermochromic hydrogels in the further in energy chemical engineering are anticipated.