All-fiber Optic Current Sensors (AFOCS) which are used to measure the power supply system in high-voltage substations have incomparable advantages to conventional current transformers, so more and more attention is paid on it. The structure of Sagnac Ringlike Optic Current Sensors (SROCS) is developed on the structure of interferometric fiber-optic gyroscope. Because of the realization of gyroscope based on the technology of Sagnac interferometers, the same way to realize SROCS becomes one of the hotspots of current transformers. The basic principle and structure of SROCS are analyzed and researched firstly. The formulation of optic current sensor is launched by the establishment of optical matrix model, and then the development condition, research results and main problems are described with emphasis on the vibration stability.