In picture sky condition is clear. Whenever i fly at night, this strange shape is there. Any idea?(Area between red lines.)

Milky Way

Really hard to see what you are referring to, but probably the 'Milky Way'

Confirmed, it's the Milky Way.Cheers,- jahman.

Thanks for replies:) i supposed that it was the one of fsx bugs, this time i have been mistaken:)