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Recent observations indicate that a high production rate of positrons (strong511 keV line) and a significant amount of excess GeV gamma-ray exist in ourGalactic bulge. The latter issue can be explained by $\sim 40$ GeV dark matterannihilation through $b \bar{b}$ channel while the former one remains amystery. On the other hand, recent studies reveal that a large amount of highdensity gas might exist near the Galactic Centre million years ago to accountfor the young, massive stars extending from 0.04 pc - 7 pc. In this article, Ipropose a new scenario and show that the 40 GeV dark matter annihilation modelcan also explain the required positron production rate (511 keV line) in thebulge due to the existence of the high density gas cloud near the supermassiveblack hole long time ago.

Electron-positron pair production near the Galactic Centre and the 511 keV emission line