With the advantages of high efficiency, low cost, and wide range of application, the energy trading mechanism designed by game theory is an effective measure to cope with the intermittency and uncertainty of the renewable energy. Meanwhile, it also makes the power gird possess more flexible demand response abilities. Under this mechanism, customers turn traditional "passive" patterns into "active" patterns while energy suppliers possess a more flexible power dispatch and distribution planning strategy. First of all, a multi-microgrid based energy trading framework is introduced where the main structure and the key elements, including load classification, processing methods of renewable energy, are briefly described. And then, the market pricing mechanism is presented by different game theoretical models in the multi-microgrid based energy trading framework. Meanwhile, the competitive relationship among the game players of the energy trading is explained. Next, by an investigation of typical real-world case studies, the energy trading mechanism of the smart grid is illusatrated. Finally, relevant multi-microgrid based energy trading problems are discussed which shows the future direction of this research.