The quantitative investigation of as-cast, as solution and ageing heat-treated microstructures of a second generation Ni-based single crystal DD11 was carried out through OM and SEM. The stress rupture properties of the alloys which had been first ageing treated under 1 100℃/140 MPa and 980℃/250 MPa respectively were also tested. The results indicate that (γ+γ') eutectic is almost dissolved when DD11 is under solution treatment of 1 320℃/6 h. And the degree of solidification segregation significantly decreases, and the alloy exhibits uniform microstructure. When the first ageing treatment temperature is lower than 1 160℃, the shape of γ' phase is cubic. But the shape transforms to sphericity when the aging temperature is higher than 1 180℃, the width of γ phase channel greatly increases, and fine γ' phase precipitates in the γ phase channel. With the increase of the first ageing treatment temperature, the stress rupture live of the alloy increases first and then decreases. The stress rupture properties are closely related to the size, the volume fraction and the morphology of γ' phase.