The evolution of objectives and the broadening of tasks have heightened the need for swift maneuverability in the photoelectric tracking and pointing system. Shifting from ground⁃based to diverse mobile platforms such as vehicles, ships, aircraft, and spacecraft marks a significant trend in the development of photoelectric tracking and pointing systems. The stabilization of the line of sight using an inertial reference unit (IRU) is essential to counteract the high⁃frequency disturbances encountered on these mobile platforms, enabling the system to achieve tracking accuracy at the micro⁃radian or even sub⁃micro⁃radian level. This paper delves into various IRU implementation strategies to mitigate disturbances from the carriers, ensuring precise aiming of the photoelectric tracking and pointing system on moving platforms. It highlights a system design that employs low noise and wideband inertial sensors for angle disturbance detection and achieves line of sight stabilization via feedback control. The document details the system's operational modes, functional features, constructs its mathematical model, and reviews both domestic and international research advancements and future directions in IRU technology. It emphasizes that inertial sensing, support structures, and control systems are critical to IRU's stabilization performance, and it organizes the latest research trends in these three vital areas. Conclusively, the paper outlines the spaceborne applications of IRU and explores potential future application domains, considering current demands.