Abstract: The microstructure and stress rupture properties at three different conditions of the second generation single crystal superalloy has been investigated. The results show that the γ matrix, γ′ phase and eutectic can be seen in the as-cast microstructure of the alloy. There are no eutectic and incipient melting and good cubic γ′ phase in the alloy after strandard heat treatment. The alloy has excellent stress rupture properties at different conditions. The fracture mechanism of stress rupture of the alloy at 760 ℃/800 MPa shows quasi-cleavage mode and the fracture mechanism at 980 ℃/250 MPa and 1100 ℃/140 MPa shows dimple model. The morphology of γ′ phase is almost no change at 760℃/780 MPa. The γ′ rafts form at 980 ℃/250 MPa and 1100 ℃/140 MPa and the thickness of rafts increases with the temperature increasing.