As one of the important devices in smart grid, all fiber optic current sensor has more significant advantages than traditional electromagnetic transformer, and has broad application prospects in high voltage and ultra-high voltage environment. Firstly, the main factors affecting the sensitivity of all fiber optic current sensor are clarified, and the solutions and research results for improving the sensitivity of current sensor by domestic and foreign scholars in recent years are summarized; Secondly, the working principle of some improved all fiber optic current sensors to eliminate the influence of temperature and linear birefringence on the sensing sensitivity is emphatically analyzed, and their main advantages and disadvantages are discussed; Finally, combined with the research status of high sensitivity all fiber current sensor, the future development trend is pointed out.