The design of key management schemes and protocols, whose main objective is to provide secure and reliable communication, is one of the most important aspects and basic research field of secure wireless sensor networks. The key management in wireless sensor networks meets many new challenges due to its intrinsic properties. In this paper, the secure and performance evaluation criterion of key management is introduced, the taxonomy for the key management schemes and protocols is proposed, the classic key management schemes and protocols are discussed and compared in detailed, and finally the open research problems and the possible solution are also pointed out. Recent related work indicates that future work will focus on some key issues such as fully distributed, self-organized, fault-tolerance and intrusion-tolerance, and location-aware etc.