By means of in-situ tension test on notched specimens of the duplex high-Nb-containing TiAl alloy and the corresponding SEM observation, the tensile fracture mechanism and crack propagation dynamic process were investigated. The results indicate that the fracture was dominated by transgranular cleavage. The fracture process was that the main crack occurred firstly, microcrack appeared and then propagated, the main crack and microcrack were linked, and the alloy fractured finally. In the crack propagation process, the obvious fracture characteristic was easy formation of microcracks in γ grains near the crack tip. For notched specimens of duplex microstructure, the stress concentrated at the notch root, and the main crack propagation path was straighter because the grain size was very fine