Advanced sensing and measurement technology is the key to realize transparent power grid and power Internet of Things. In order to meet the measurement needs of the power Internet of Things, this paper developed a micro current sensor device based on giant magnetoresistance effect, including the design of the sensor architecture, signal processing circuit, digital processing circuit, self energy, wireless communication, temperature compensation and other functional modules, the sensor shell structure is designed and the special protection design of IP and insulation is carried out. Finally, the sensor has been applied in the field of low-voltage distribution for a long time. The results show that the current sensor can work stably and reliably for a long time. It has the advantages of miniaturization, high integration, convenient installation and remote management. It can provide more comprehensive and real-time information support for the operation of the distribution network and lay the foundation for the transparent management of the smart grid.