Abstract: The initiation and propagation of small cracks in Ti-46Al-4Nb-1.8Cr-0.2Ta alloy at high temperature were studied. The samples of smooth plate were subjected to fatigue test at 750 ℃, stress ratio R=0.1, frequency 4 Hz on the in-situ testing machine, and the crack micro-topography was observed by scanning electron microscopy. The results show that the fatigue crack of the TiAl alloys in the lamellar structure is most likely to initiate in the lamellae and the plastic deformation is accompanied with the fatigue during the lamella formation. The root of circular notch is most inclined to initiate crack at the stress concentration area with 45° to the horizontal direction. The main crack is formed by the combination of the cracks in the lamellar boundaries and the cracks in the lamellae during the fatigue process and extends in a direction perpendicular to the direction of the load. In the late stage of fatigue crack growth, the crack propagates through the layer.