Abstract: The purpose of this paper is to estimate the fatigue crack growth threshold of a high-Nb TiAl alloy at the different temperatures based on scanning electron microscopy (SEM) in-situ observation. The results indicated that the fatigue crack growth threshold ΔK_th of a nearly lamellar high-Nb TiAl alloy with 8% Nb content at room temperature and 750℃ was determined as 12.89 MPa·m^1/2 and 8.69 MPa·m^1/2, respectively. The effect of the elevated temperature on the fatigue crack growth threshold cannot be ignored. At the same time, the early stage of fatigue crack propagation exhibited multicrack initiation and bridge-link behavior.