Abstract: In the energy, chemical, and environmental sectors, advancements in high-temperature, high-pressure, and energy-efficient technologies have heightened the issue of metal corrosion in complex aqueous environments. This has become a key bottleneck restricting the technological innovation and safe operation of industrial equipment. In complex high-temperature and high-pressure aqueous environments, the presence of dissolved oxygen, corrosive gases (CO₂ and H₂S), and various corrosive ions (Cl^– and SO₄^2–) synergistically enhance the corrosion rate of metal materials—often by several to dozens of times compared to ambient conditions (room temperature and normal pressure)—posing a serious threat to the service life and operational safety of energy and chemical equipment. In many corrosion protection technologies, corrosion inhibitors are efficient and economical means of corrosion protection, and their application in high-temperature and high-pressure complex aqueous environments has become a cutting-edge hotspot in the field of material corrosion protection. This paper presents a systematic review of inorganic and organic corrosion inhibitors used in high-temperature, high-pressure, and even sub/supercritical aqueous environments. Nitrites, despite their insufficient high-temperature stability, still have application prospects. Phosphates can be used in supercritical aqueous environments, but excessive dosages can easily cause corrosion of molten salts. Imidazolines have excellent high-temperature performance and can be used in extreme environments. Quaternary ammonium compounds have numerous derivatives and can be used in complex high-temperature and high-pressure aqueous environments. Furthermore, film-forming amine compounds have good film-forming properties even under supercritical water conditions. Through an in-depth analysis of various types of corrosion inhibitors in different corrosive media and their corrosion inhibition mechanisms, it was concluded that key factors determining corrosion inhibition performance include the molecular structural stability of the corrosion inhibitor, its adsorption capacity on the metal surface, and its tolerance to the surrounding environmental conditions. Although many studies have confirmed that most corrosion inhibitors exhibit high rates of corrosion inhibition under ambient conditions, their performance in complex high-temperature and high-pressure aqueous environments remains insufficiently explored. Due to limitations in high-temperature online monitoring technology, research on current corrosion inhibitors under such extreme conditions is still limited. Moreover, existing corrosion inhibitors often suffer from poor stability, short-lived effectiveness, and other performance issues. This review can provide an important reference for the reasonable selection and optimization of corrosion inhibitors under extreme working conditions. Moving forward, it is essential to investigate the long-term stability of corrosion inhibitors under extreme conditions and their corrosion inhibition mechanism in complex high-temperature and high-pressure aqueous environments, as well as to explore the compounding and synergistic effects of inhibitor combinations. There is also an urgent need to develop new types of corrosion inhibitors that combine high-efficient corrosion inhibition performance with environmental compatibility to meet the growing demands for corrosion protection in high-end equipment across the energy, chemical, and other related industries. The development of new corrosion inhibitors that offer both efficient corrosion inhibition performance and environmental friendliness is essential to meet the urgent need for protecting high-end equipment in the energy and chemical industries.