This paper presents a monitoring system of building electricity using IPv6 to establish a network. This smart metering system consists of three parts: the host software, the network and the sensor nodes. The network, whose data transmits via Zigbee wireless communication protocol, is designed based-on IPv6 protocol, and builds the IPv6 protocol on IEEE 802.15.4 wireless network. The Sensor node has a unique IP address and the sampling rate is set according to the host system. With real-time measurement of power, current and voltage values including RMS, instantaneous value and peak value, each node achieved accurate data sampling and communication stability. The host software is designed for building test characteristics, having a tree hierarchy and friendly interface to user. The reliability and accuracy of this monitoring system are verified in the experiment.