The reliability of the fiber Bragg grating (FBG) sensors embedded in textile composites with both dual-end and single-end is studied in this paper. The effects of debonding of the interfaces of the fiber/coating and coating/resin on the reliability are considered. Measurement error induced by the deviation of the location of sensors after embedding into a composite has been analyzed for the three-point bending experiments. The analysis indicates that the determination of the precise location of FBG sensors would be a key problem when the sensors are embedded in a large gradient strain field. The experimental results show that the debonding at the interfaces has great effect on the reliability of single-ended FBG sensors and little effect on that of dual-ended sensors. It is suggested that FBG sensors be calibrated before they are imbedded into composite, which will help to improve the precision of the measurement and avoid damage to sensors to ensure the sensor's strength while the composite is under loading.