The effect of uniaxial stress aging at 1 070℃/100 MPa on the microstructural evolution and the stress rupture properties of a single crystal supperalloy DD11 was investigated.The microstructure before and after the stress aging was observed with scanning electron microscope and transmission electron microscope,and the stress rupture properties before and after the stress aging were also tested.The experiment results show that the evolution of the microstructure can be divided into two stages,rafting (first 50 h) and coarsening (after the first 50 h) of the rafting microstructure.At the first stage,the vertical direction of the γ phase channels becomes narrow or disappears gradually,and the width of horizontal direction of the γ phase channels increases gradually.At the same time,the cuboidal γ'phase expands horizontally and gradually connects with each other.At the second stage,the dimension of the rafts coarsens slightly.However,the morphology of rafting keeps stable.The stress rupture properties of 1 070℃/140 MPa decrease slightly at first stage and degrade gradually at second stage.After stress aging for 500 h,the stress rupture properties decline from initial 360 h to 140 h.The results show that the key factors for the degeneration of the stress rupture properties are the coarsening of the matrix channels and the rafting of the microstructure.