Creep tests at 1150 ℃ , 80 – 150 MPa were carried out in a 3rd generation single crystal superalloy DD33. The fracture morphology and damage characteristics in longitudinal section were studied by SEM, EBSD, EDS and TEM. The effect of stress on the fracture mechanisms was analyzed. The results show that the casting pores near the fracture are almost polyhedral, and cracks initiated at the corner of pores. Compared with the lower stress, more creep pores and cracks were induced at 150 MPa. Besides, at 80 MPa, the γ/γ′ matrix bears an extra 35 MPa effective stress due to the thick oxidation affected zone. The highly-localized topologically close-packed (TCP) phase can be found nearby the fracture, and some pores as well as cracks exist at TCP/γ′ interface. With the further increase of applied stress, more surface cracks penetrate into the matrix and more carbides are cracked. Thus, the final failure of the alloy not only directly relates to the internal pores and the pore-induced cracks, but also the effect of the oxidation affected zone, surface cracks penetrating into the matrix, cracks at TCP/γ′ interface and cracked carbides should be considered.