The segmented mirror active optics technology is one of the key technologies for the extremely large telescope, while edge sensor is one of the essential core components of active optics for the co-phasing maintenance of all segmented mirrors. The main properties of these edge sensors are of high precision of nanometers, high linearity, and low sensitivity to temperature and humidity fluctuations as well as high reliability. This paper presents an eddy current edge sensor design developed cooperatively by Nanjing Institute of Astronomical Optics & Technology and University of Science and Technology of China. The stage work performance results of eddy current sensor prototype under representative operational conditions are also presented.