A high-precision fiber Bragg grating dislocation sensor, including a fiber Bragg grating, a loose tube, a tension spring, a sliding rod, a positioning piece, a sheath, a stainless steel tube, a transmission rod and a fastener. The sliding rod, the tension spring, the positioning piece, the fiber Bragg grating and the sheath are connected in series, and are provided in the precision stainless steel tube successively. The mechanism of the dislocation sensor is that an elastic force, converted from the local uneven settlement of the settlement joint, is applied on the bare fiber Bragg grating, so that the bare fiber Bragg grating suffers an axial stress and a strain is generated by itself, and the central wavelength of the fiber Bragg grating is further changed, allowing for the monitoring of settlement.