Barrier exists in every stage of developing a smart grid，from fundamental science and engineering technology research to development，demonstration and operation.Figuring out the critical barrier will be helpful to clarifying how to maximize smart grid's potential，thus providing comprehensive social and economic benefits to the nation.This paper identifies eleven key challenging issues of the smart grid and emphasizes that metrology and standardization are the priority important areas，interdisciplinary cooperative research is the inevitable choice for developing the smart grid，while legal framework and supervision，market design and management reform are the basic guarantees of successfully implementing the smart grid and obtaining the deserved benefits.