Abstract: As the transmission voltages are increased up to ultra high voltages (UHV) and even high voltages (EHV), more and more intrinsic shortcomings, which are hard to overcome, of traditional current transformers (CTs) have been revealed. Therefore, it is an obvious trend that using electronic current transformers (ECTs) to replace traditional CTs. Especially, in the situations of that smart grid is advocating at present in electrical power systems, the demand of electrical systems for fiber-optic current transformer (FOCT) is increasing day by day. Besides, fiber-optic current sensors (FOCSs) have also many applications in areas of high freqency current and weak current measurement. After introducing to the basic concept and clasifications of FOCTs, the main technical hinders encountered in the realization procedure of FOCTs are elaborated, the possible solutions for the hinders are inquired into. Finally, applications of some new technologies, such as fiber Bragg gratings(FBG), quantum dot doped fibers, and fiber nanowires/microwires etc., in FOCSs are presented.