In order to solve the practical problem of low displacement sensitivity when a cantilever beam or deformed ring is used as an elastic deformation structure of a fiber Bragg grating displacement sensor, a new elliptical displacement amplification mechanism was chosen to amplify the mini-shifting of the displacement, and the displacement resolution of the sensor was adjusted by changing the mechanical size of the elliptical amplifier. When the length of the elliptical displacement amplifying structure is 60 mm, the width is 19.8 mm, and the maximum width in the middle is 30 mm, the magnification of the mechanical displacement is amplified by 2 times. When the range changes from 0 to 100 nm, the resolution of the fiber Bragg grating displacement sensor measured in the experiment is 6.1 pm/mm, and the linear correlation coefficient of displacement and corresponding wavelength shift is 0.998 52. The sensor can be effectively applied to high-precision on-line monitoring for structural displacement of mechanical equipment and civil engineering.