Abstract: Microstructure of gas turbine blade made of DZ411 alloy after cumulative operation for 2 700 h was analyzed and compared with the original microstructure. Combining with change of γ' phase in microstructure of DZ411 alloy rod after long-term thermal exposure at 900 ℃ and stress-rupture at 850 ℃ under different stresses (220, 260, 280, 300 MPa), service temperatures of the gas turbine blade were evaluated. The results show that after cumulative operation for 2 700 h, the microstructure at most positions in the blade exhibited no obvious degradation, indicating that the operation temperature at these positions was below 850 ℃. In a small number of areas at leading edge on section near blade tip, the γ' phase degradation at early stage was observed, and therefor it was deduced that these areas might be subjected to short-term high temperatures and the maximum temperature was higher than 900 ℃.