According to the research on Sagnac effect and the interference structure of fiber Sagnac loop, the improved schemes of fiber Sagnac loop are introduced in recent years. The plenty of experiments are implemented and the application range is enlarged greatly. Based on the basic principle of Sagnac effect, the main applications and newest developments of fiber Sagnac loop at present stage such as fiber gyro, fiber hydrophone and Sagnac loop filter are summarized. The advanced and new technology directions of fiber Sagnac loop such as changing the structure of Sagnac loop, adding medium to Sagnac loop, cascading with other structure, making full-light cache and multiple-wavelength fiber lasers are introduced finally.