Energy is one of the most important parts of wireless sensor network design. Effective estimate the residual power of sensor nodes can be used to aid select the all-round and optimal schemes for applications and router protocols design, which can notably promote the survival period of wireless sensor networks. By software based real time energy estimation to scale the power consume of nodes can conciliate the deficiency of hardware. However, because node energy loss is nonlinear, so software based real time estimation inevitably not accurate. On the contrary, hardware based method scale residual energy in terms of reliability, efficiency and accuracy are relatively better.