Deformation monitoring is an important means to predict and forewarn slope geologic disaster. To overcome the drawbacks in the current deep displacement monitoring of slopes, a novel clinometer based on fiber Bragg grating sensing technology was developed. The FBG clinometer sensor comprises a rigid unit, a flexible unit for sensing and the connecting hinge. The flexible sensing unit is an equalstrength beam structure with a fiber Bragg grating, and the FBG adopts a symmetric arrangement on the beam surface to eliminate the influence of temperature on the measurement. The rigid unit will have relative deflection at the joint when the rock and soil inside the slope are deformed. Based on the FBG wavelength offset in the flexible sensing unit and the linear relationship between the central wavelength of FBG and strain and angle, the relative deflection angle between the rigid units can be obtained, and the deep deformation monitoring of the slop can realized. The experiment indicates that the measuring unit of the developed inclinometer has good linearity, high sensitivity and resolution, and the error caused by temperature is small.