For real-time monitoring of engineering structure, according to the principle of displacement sensing, a fiber Bragg grating(FBG) displacement sensor with tension cantilever beam is designed. During the displacement measurement, the relative displacement of the fulcrum at both ends of the sensor is generated, and the displacement is transmitted to the cantilever beam through the spring. The displacement is measured by measuring the strain of the cantilever beam. The sensitivity can be adjusted by changing the section size and length of the cantilever beam, the size of the cantilever beam is determined according to the technological constraints and theoretical calculation, and the aperture value is determined through the finite element analysis of the effect of the aperture size of the cantilever beam end on its strain. Finally, the performance of the sensor is tested, the results show that the sensitivity of the FBG displacement sensor with tension cantilever beam is 101.3 pm/mm, and the measuring range can reach 30 mm. Compared with the general commercial FBG displacement sensor, the sensitivity of FBG displacement sensor with tension cantilever beam is greatly improved, and the linear fitting degree reaches 0.994.