Wireless sensor networks consist of a set of connected devices deployed to report sensitive environmental data. Key management in wireless sensor networks remains a challenging issue due to the limited resource capacity of devices. Most existing solutions focus only on the key storage and updating optimization giving less attention to the mobility, which is more needed in the nowadays applications. In this paper, we propose a secure and efficient key management system with mobility support. The proposed scheme is based on hybrid key establishment to meet both the robustness and efficiency requirements. The sensor nodes can be mobile, where they could leave, rejoin their cluster, or join other ones. We incorporate lightweight techniques for sensor node integration, departure, revocation and key updating. Its efficiency is evaluated by comparison with other concurrent schemes, where it demonstrates the best results.