Traditional network laying based network protocol can result in waste of physical performance of the sensor and cause drop of the whole performance of the network. A key management scheme for heterogeneous sensor networks based on residual energy of nodes is proposed, which balances the energy consumption among the sensors and prolonged networks lifetime. Next hop node in the forwarder space of the sensor is selected based on rest energy, node degree and so on. Meanwhile, a shared secret between two nodes is established through key exchange to make their communication more secure and trusted. The scheme combines route relation at the network layer with key relation of nodes at the application layer effectively, which realizes crosslayer design of key management. The experimental results show that the proposed algorithm guarantees key connectivity while balances energy of nodes and extends the lifetime of wireless sensor networks.