Interrupted and ruptured creep tests were carried out on single crystal superalloy DD9 at 980℃/250MPa and 1100℃/137MPa. Microstructure evolution during creep was analyzed through scanning electron microscope, transmission electron microscope. The microstructure evolutions are similar under the creep conditions. Cubical γ′ phase dispersedly distributed in γ matrix gradually evolves into layered structure perpendicular to the stress direction. The width of γ matrix channel along the direction parallel to the stress increases. The relationship between the increase in width of γ matrix channel and the strain satisfies linearity in logarithmic form, indicating that the width of γ matrix may be inferred via the strain under creep at high temperature and low stress. This provides an alternative way to illustrate the increase in width of γ matrix for single crystal superalloys during creep under high temperature and low stress. In the early creep stage, dislocations formed in γ phase generate mutually perpendicular networks through cross slip at γ/γ′ interface. Then stable hexagonal dislocation networks form as a result of coupling effects of external stress and mismatch stress under elevated temperature. In the later period creep, dislocations shear γ′ phase, ultimately causing the fracture.