Conventional method of displacement monitoring has some limitations,so this pape r presents a new fiber Bragg grating (FBG) displacement sensor based on wedge cavity structure.The new FBG displacement sensor has the advantages of simple structur e,small size, anti-electromagnetic interference and the adjustable measurement accuracy.Calib ration of the FBG displacement sensor is carried out.The results show that the sensitivity of this sensor is 13.77pm/mm,the correlation coefficient is up to 0.99and the linearity is good.The FBG displacement sensor is used in test of reinforced con crete column under biaxial eccentric loads.The monitoring results of the FBG displacement sensor are compared with those of the traditional electric displacement meter,proving the FBG displacement sensor has good accuracy.It is suitable for long-term project structure monitoring.