The communication between the power supplier and power customers is a key issue in smart grid. Current power systems are based on a solid information and communication infrastructure, while the wireless communication environments of the smart grid face much more new challenges in terms of reliability, efficiency and so on. This paper addresses critical issues on smart grid technologies primarily in terms of communication technology issues and opportunities. The main object of this paper is to provide an overview at the current state of the communication technologies for smart grid, and discuss the still-open research issues in this field. Furthermore, since the resources scarcity is the crisis of communication systems in smart grid, the cognitive radio based communication network architecture is proposed to take the potential spectrum advantages.