To more in depth understand the doping effects of oxygen on Si Ge alloys, both the micro-structure and properties of O-doped Si Ge(including: bulk,(001) surface, and(110) surface) are calculated by DFT + U method in the present work.The calculated results are as follows.(i) The(110) surface is the main exposing surface of Si Ge, in which O impurity prefers to occupy the surface vacancy sites.(ii) For O interstitial doping on Si Ge(110) surface, the existences of energy states caused by O doping in the band gap not only enhance the infrared light absorption, but also improve the behaviors of photo-generated carriers.(iii) The finding about decreased surface work function of O-doped Si Ge(110) surface can confirm previous experimental observations.(iv) In all cases, O doing mainly induces the electronic structures near the band gap to vary, but is not directly involved in these variations. Therefore, these findings in the present work not only can provide further explanation and analysis for the corresponding underlying mechanism for some of the experimental findings reported in the literature, but also conduce to the development of μc-Si Ge-based solar cells in the future. To more in depth understand the doping effects of oxygen on Si Ge alloys, both of the micro-structure and properties of O-doped Si Ge (including: bulk, (001) surface, and (110) surface) (i) The (110) surface is the main exposing surface of Si Ge, in which O impurity prefers to occupy the surface vacancy sites. (ii) For O interstitial doping on Si Ge (110) surface, the existences of energy states caused by O doping in the band gap not only enhance the infrared light absorption, but also improve the behaviors of photo-generated carriers. (Iii) The finding about decreased surface work function of O-doped Si Ge (110) surface can confirm previous experimental observations. (Iv) In all cases, O do mainly induces the electronic structures near the band gap to vary, but is not directly involved in these variations. Therefore, these findings in the present work not only can provide further explanation and analysis for the corresponding underlying mechanism for some of the experimental findings reported in the literature, but also conduce to the development of μc-Si Ge-based solar cells in the future.