Fossil and other traditional energy have been bringing serious challenges on energy consumption. Making full use of clean and renewable energy becomes the inevitable requirement of social development. With the development of smart grids, micro-networks and the rapidly developing Internet technology, researchers put forward the concept of energy internet synthesizing the energy network and information network, which aims to improve the energy efficiency, realize the mutual complementary of multiple energies, promote the change of energy usage, and provide new paradigm for sustainable energy development. First of all, this paper summarizes the state-of-the-art researches on energy internet in different countries. Then, in the view of optimal operation of energy internet, optimization operation models, communication and data for the optimal operation of energy internet, and the fault propagation mechanism in energy internet optimization operation are investigated. furthermore, this paper points out the significant research direction and the key techniques for the optimization operation of the energy internet, in order to provide a potential help for China's Energy Internet research.