All-fiber optic current sensor is applied for micro-current detection, which can expand the application of optical fiber sensing technology in weak magnetic field detection. On the basis of analyzing the basic principle and main optical path structure of the all-fiber microcurrent sensor, the latest research results of the all-fiber microcurrent sensor are reviewed from three aspects: increasing the number of optical circuit cycles, improving the performance of the sensing fiber, and reducing the system noise. And the future development trend of all-fiber microcurrent sensor is prospected.