Abstract: Ti₂Al Nb alloy has significant applications in the aerospace field due to its excellent high-temperature performance and low density. The high temperature creep resistance and fracture mechanisms of the Ti₂Al Nb alloy in the temperature range of 700-800 ℃ were systematically investigated and the effects of different preheat exposure treatments before creep test were explored. The results indicate that the precipitation of the β phase during preheat exposure treatment induces grain boundary embrittlement, which leads to the deterioration of creep resistance of the Ti₂Al Nb alloy at 700 ℃. And the increase of the preheat exposure temperature further intensifies the degree of deterioration. However, at higher creep temperature of 750-800 ℃, the detrimental effect of preheat exposure on the alloy’s creep resistance is weakened. This is related to the change of the fracture mechanism of the alloy when the creep temperature increases, the failure mode gradually shifts from ductile fracture to brittle fracture. Additionally, at the same creep temperature, the fracture surfaces of the alloy with different preheat exposure treatments tend to exhibit similar fracture characteristics.