In order to meet the need of slope monitoring,a new fiber Bragg grating(FBG)differential tilt sensor combining mercury column and piston is proposed.When the tilt angle of measured object changes,the pressure to the piston changes as the effective mercury column length changes in the metal shell.The pressure of the mercury is passed to the free end of the cantilever beam by the piston and leads to the central wavelength change of FBG,which is pasted on the left and right ends of the cantilever beam.By use o...