Traditional electromagnetic induction current transformers have problems such as large and complex structure, slow response speed, and low safety level, so scholars combine various sensing technologies with optical fibers to explore optical current transformers that can become the main application of power systems in the future. With the mature development of optoelectronic technology, optical current transformers came into being. It has outstanding advantages such as high sensitivity, high integration, high stability and the ability to work in complex environments. In view of the classification of optical current transformers according to different principles, the research status of the principle, structure, manufacturing technology and signal processing of all-fiber current transformers, current transformers based on magnetostrictive effect, current transformers based on magnetostrictive effect, current transformers based on magneto-optical effect, and current transformers based on thermal effect are reviewed, and their future development trends are predicted.