Recently with the invention of fiber optic Bragg grating (FBG), new kind of sensors based on FBG is increasingly challengingly the dominating position of some traditional sensors, because this new device has some intrinsic capability: Such as multiplexing, self- referencing, optical and mechanical reliability, anti-interference. Especially it brings the significant advantages that they are non- conductive and lightweight, which can allow for much simpler insulation and mounting designs as the application voltage up to 1000kV or more to day. In addition, it doesn't exhibit hysteresis and provide a much large dynamic range and frequency response than iron- core conventional current transformer (CT). In this paper a current sense device based on electromagnetic force is presented. A FBG is held on the armature of an electromagnetism by one end. As current pass through the iron coil, the magnetic force of the coil lengthens the FBG. Then the Bragg wavelength will change via current. By measuring the change of Bragg wavelength of the FBG we can build a relationship between the tested current and the Bragg wavelength. In this paper the configuration of the new device, the theoretical analysis and measurement results are given.