In order to solve the excessive computation and storage requirement arising due to the frequent sensor nodes movement in WSN, a new public key has been proposed based on ECC key agreement protocol. The mutual authentication and agreement on a session key can be realized between users, or between user and a network server in WSN. This protocol adopts ECC techniques to consult session keys and AES Symmetrical encryption technology to achieve confidentiality. Compared with traditional protocol, this protocol could provide greater security with relatively fewer bits and reduce the requirement of computation and storage. A protocol has been proved to be a secure authenticated key agreement in ID-BIM models. Results show that it provides a perfect forward/back secrecy and PKG forward secrecy.