Since its emergence, smart grid has been given increasingly widespread attentions. Basically, smart grid combines a various modern technologies like network communication, information processing and distributed control to provide a more secure, reliable and intelligent grid, thus meeting the requirements of future social and economic development. As a new paradigm in the power grid, smart grid undoubtedly represents the mainstream trend of future electric industry. As a result, it also brings some new technical challenges to researchers and engineering practioners. To support researchers and engineering practioners constructing a modern and intelligent grid, research in the field of smart grid has proliferated. In this paper, we look deeper into some key issues of smart grid, such as distributed cooperation and control, data and application integration, and knowledge-based comprehensive decision. Still, we give some solutions to resolve these challenges. In addition, we also introduce the concept of smart grid and define its key characteristics. Finally, we outline future directions of research and conclude the paper.