A multi-longitudinal-mode Bragg reflector (DBR) fiber laser based displacement sensor is reported and implemented. Using cantilever structure,the fiber laser sensor is on the basis of beat frequency demodulation. When the free end of cantilever has a displacement,the longitudinal mode beat (LMB) will change correspondingly. Within the displacement range of -60.17-59.75 mm,the LMB changes from 273.85-272.908 MHz linearly,with a linearity of 0.9993,which agrees with the theoretically analysis. The sensor has a high repeatability and a precision of 3.8×10-3 mm.