Abstract: The superior high temperature performance and creep resistance of high Nb-TiAl alloy make it very promising as aeroengine structural materials. In this paper, a water-cooled copper crucible vacuum induction melting furnace(ISM) was used to prepare Ti-43Al-6Nb-1Mo-1Cr-0.1C(T43-0.1C), Ti-43Al-6Nb-1Mo-1Cr-0.05Y₂O₃ (T43-0.05Y₂O₃) two alloys, the high temperature tensile properties and creep resistance of two high Nb-TiAl alloys have been studied. The tensile properties and creep properties of the two alloys at a high temperature of 850℃ were tested. The deformation zone structure and fracture morphology of the two alloys were observed by scanning electron microscopy and transmission electron microscopy. The fracture mechanism was studied and the C and Y₂O₃ in high Nb-TiAl were analyzed. The strengthening mechanism of the alloy. The results show that the maximum strain of T43-0.1C is 4.380%, the maximum tensile strength is 577.78MPa, the maximum strain of T43-0.05Y₂O₃ alloy is 12.30%, and the maximum tensile strength is 620.22MPa under 850℃ tension. The alloy fractures in a combination of brittleness and toughness at a high temperature of 850℃. The strengthening of the T43-0.1C alloy mainly comes from the solid solution strengthening of C, but 0.1C reduces the room temperature plasticity. The strengthening of the T43-0.05Y₂O₃ alloy mainly comes from the fine grain strengthening of the Y₂O₃ particles and the second phase strengthening. The creep performance of T43-0.1C alloy is better than T43-0.05Y₂O₃ alloy at 850°C.The fracture mechanism of T43-0.1C alloy is the initiation and propagation of cracks at the grain boundary, which eventually causes the separation of the grain boundary. The fracture mechanism of T43-0.05 Y₂O₃ alloy is void nucleation, growth, and interconnection.