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 of the finite element method, the stress characteristics of the cantilever beam and FBG are analyzed with two point bonding method at different tilt angles. According to the simulation parameters, the tilt sensor is developed. Angle calibration test and temperature sensitivity test are carried out on the sensor. Experimental results show that the measuring range of the FBG tilt sensor is 0°-40°; sensitivity is 21.8 pm/(°); the fitting degree R2 is 0.998, and the repeatability is 1.12%.