Abstract: Under extreme operating conditions, such as high velocity, elevated temperatures, intense pressure and severe oxidation, the internal surfaces of mechanical components are persistently confronted with daunting challenges posed by wear and corrosion. To address these challenges effectively, internal diameter thermal spraying techniques have been widely studied and applied. The technology is specifically aimed at the inner surface of the workpiece to enhance the service life of the workpiece through the spraying of wear-resistant or anti-corrosion coatings. Four pivotal internal diameter thermal spraying techniques including internal diameter-plasma spraying, internal diameter-transferred wire arc spraying, internal diameter-high velocity oxygen/air flame spraying and internal diameter-wire arc spraying were reviewed, the characteristics, advantages and disadvantages of these technologies were comprehensively analyzed from multiple dimensions such as technical principle,operation mode, development process and their applications in industrial fields. The challenges and solutions of internal hole thermal spraying technology in engineering applications were further discussed. It is pointed out that the future research focus is to develop new coating technology and materials, as well as the use of numerical simulation technology to predict and optimize coating performance.