A series of axial force controlled fatigue tests at 1070℃ had been performed to elucidate the influence of stress ratio (-1/-0.33/0.1/0.5/0.8) on high cycle fatigue behavior of DD6 single crystal superalloy. In order to analyze the fracture micro-mechanism under different stress ratio, fracture morphology and microstructure of these samples were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Experimental results indicate that the high cycle fatigue life of DD6 alloy with different stress ratio decreases with the increase of stress amplitude and mean stress. When the stress amplitude is constant, the fatigue life of DD6 alloy decreases with the increase stress ratio. The fatigue life of DD6 alloy increases with the increase stress ratio when the mean stress is constant and the stress ratio is less than 0.5. However, when the mean stress increases to a certain extent, the stress ratio has no significant effect on the fatigue of the alloy. Analysis on fracture surfaces of DD6 alloy at 1070℃ demonstrates that that quasi-cleavage mode is observed under the condition of low stress ratio, but is dimple mode at high stress ratio. The fatigue fracture mode under medium stress ratio has the mixing characteristics of the above mentioned mode. High temperature oxidation under low stress ratio is helpful to the initiation and propagate of cracks.