Wireless sensor networks are used widely in many environments which require various key management schemes to provide security services. A novel hiberarchy cluster model is proposed, based on which, some new techniques are given to realize a key management scheme that has characters of low-energy and high security. Main advantages of the scheme include: 1, Using a hiberarchy cluster model in the deployment of small-scale wireless sensor network, and the model can decrease energy consumption of networks effectively; 2, Based on two key chains, presenting a method of establishing pairwise keys, which not only can build good secure connectivity among sensor nodes, but also can support adding new sensors into networks; 3, Designing a new method to deliver cluster key, which can deliver cluster key by only one time broadcasts; 4, The whole key management is resilient to compromise of sensors.