This paper proposes a double-beam complementary fiber Bragg grating (FBG) displacement sensor to achieve the measurement of positive and negative bidirectional displacement.The double "cantilever beam + wedge-shaped slider" structure is adopted,when one cantilever beam is deformed by displacement,the other cantilever beam is not deformed and provides temperature compensation function.The two cantilever beams are in zero bend when the sensor is in zero value measurement point state,and the twin beams are temperature compensated for each other,eliminating temperature effects.The performance test experiments prove that the sensitivity of the sensor is 29.369 pm/mm within a range of ±50 and the measurement repeatability is good.Eight sensors are manufactured for deformation safety monitoring of a city metro,and deformation measurements are carried out in three areas:track bed settlement,track bed annulus and segment annulus.During the long-term monitoring period,the sensor workes stably and the deformation state of the monitored structure is stable,indicating that the sensor has good measurement performance and it is applicable to long-term structural health monitoring.