Abstarct: Determining of the energy of a molecule has always been interesting to chemistry scientists and they have always used integrals to calculate them. Since graphs have been used to display the structure of molecules, mathematical scientists have tried to use graph properties to calculate molecule energy and find a simpler way to determine it. The calculated quality is called graph energy which is almost equal to the energy of molecule. In the thesis we have tried to study the subjects related to the energy of different graphs and explain a classification for that.