All-inorganic perovskites with improved stability are expected to be better candidates for optoelectronics, compared to organic-inorganic hybrid perovskites. A new member of all-inorganic perovskites, CsPb2Br5, has attracted great attention for its promising applications in optoelectronic devices. However, the origins of the green emission in CsPb2Br5 have been actively debated. By using first-principles calculations, we find that CsPb and VBr are dominant intrinsic defects independent of the growth conditions within the stable region of CsPb2Br5. Interestingly, we suggest that individual intrinsic defects do not lead to the green emission of CsPb2Br5, while the donor-acceptor pair recombination of CsPb and VBr possibly does. Our findings provide new insights into the experimental controversy about the green emission and its origins in CsPb2Br5 from the perspective of intrinsic defects, which help to extend the application of CsPb2Br5 in optoelectronic devices.