It was found that the universe is inflating with accelerated speed in 1998. But until today there is no theory to explain it. This time, a stationary space model instead of inflating model was made up that accounts for the cause of galaxies’ leaving each other with accelerating speed, by presuming space is equivalent to elementary particles. Also it explains gravity generation. Gravity and dark energy are created at the same time of a star formation by space’s change to elementary particles. After space changed to elementary particles around the center of the universe, it is transported to the verge of the universe. And around the verge of the universe, stars and galaxies change back to energy body again, after bursting into elementary particles. This is the space convection system. And the interaction by gravity or dark energy is caused by the energy level difference of energy body.