In the paper, the damage of the SiC_f/Ti6242 composite in the thermomechanical fatigue test was monitored by the acoustic emission technique and the high-resolution X-ray tomography. The thermomechanical fatigue test was conducted with a trapezoidal waveform to simulate the actual loading of the bladed ring. The applied stress range is 130–1300 MPa and the temperature range is 100–500 °C. The maximum stress was held for 2 min at 500 °C. The AE events emerged mainly in the loading stage and the dwell stage for the cycle where the AE signals of fiber fracture and matrix cracking were found. The matrix cracks of the unbroken specimen were detected by the high-resolution X-ray tomography. The necking of the tungsten filament in the broken fiber in the cracking region was also found. These results show that the damage mechanism of the specimen is dominated by a mixture of fiber fracture and matrix cracking.