With the development of Wireless Sensor Network (WSN) technology, it has been adopted in a wide variety of applications such as the health care system and so on. Yet, there are still some problems need to be addressed, one of which is the security issue. A lot of schemes from different points of view were proposed to ensure the security in WSNs, however, most of them are proposed for static networks while it is less to consider the situation for the security of the dynamic topology update. The authors' paper is a novel key management scheme for the dynamic WSNs. The security authentication and random key distribution were initialized in the network deployment phase.