This paper is concluded that， with the breakthrough and wide implementation of energy storage， different form energy converting and mutually alternative technologies， the power grid will more serve as a game platform for different energy resources than a traditional power transmission， transformation， and distribution grid. According to the main functions and key technologies， the evolution procedure is divided as three stages: strong inter-connective， open and interactive， flexible and controllable. As the production of this procedure， the smart grids initiated in China， America and Europe are analyzed. It is hard to foresee the long term form of future grid， but its characteristics such as interconnected grid， energy carrier will be further exploited fully.