what would have happened if instead of the sun ,the earth would have been the centre of the solar system.

The sun is at the center of our solar system. It is responsible for our earth's climate and weather. And also it is a prime source of energy, Sun being in the centre is the major source of energy and power for all the planets of solar system. If earth would have been the centre of the solar system, then it would directly impact on the climate and weather of the earth. 
The shift in the Sun's position would directly impact the climatic condition and the energy which it provides to other planets.