The advent of synchrotron radiation facilities has provided a new approach for characterizing the internal microstructures of materials. To apply synchrotron radiation facilities to material fatigue research, several fatigue testing apparatuses coupled with synchrotron radiation facilities have been developed. However, these testing apparatuses are often constrained by factors such as loading frequency, specimen size, and imaging characterization. To address the limitations of traditional in situ fatigue testing apparatuses, a high-temperature and high-frequency in situ diffraction and imaging fatigue testing apparatus based on a synchrotron radiation source has been developed. A high-frequency fatigue loading module and an ultrasonic fatigue loading module are employed. Moreover, 20~1 000 Hz and (20 ±0.5) kHz wide-frequency-domain fatigue loading can be achieved, enabling low-cycle, high-cycle, and very-high-cycle fatigue experiments within the limited loading time. The apparatus supports both ambient and elevated-temperature testing. The high-temperature mode employs high-frequency induction heating with real-time infrared temperature monitoring, which is dynamically regulated via proportional-integral-derivative (PID) control to enable experiments within the 400~1 000 ℃ range. A wide range of fatigue specimen dimensions can be accommodated, facilitating the incorporation of the influence of scale effects on material properties and behavior. A series of in situ diffraction, imaging, and collaborative experiments were conducted on the developed in situ fatigue testing apparatus and the BL16U2 beamline at the Shanghai synchrotron radiation facility

(SSRF). The results indicate that the in situ fatigue testing apparatus developed in this study enables dynamic characterization of internal defects in materials during the fatigue process, nondestructive 3D morphology characterization of internal defects and cracks, and multidimensional synergistic characterization of diffraction and imaging during fatigue, which can provide an excellent research platform for studying the internal damage evolution behavior of materials during fatigue.