The existing slope safety monitoring studies mainly focus on long-term monitoring of slowly evolving horizontal deformations. However, during the practical applications, sudden deformations may also lead to landslides due to the natural and man-made trigger factors. This article first proposes a reusable and distributed fiber Bragg grating (FBG) inclinometer for simultaneous measurement of horizontal deformation and vibration induced by sudden deformation, providing more extensive monitoring for slopes. The proposed inclinometer utilizes ten FBG tilt sensors in series as measuring elements, which are characterized by easy installation and removal, thus making them reusable and eliminating excessive waste. A signal decomposition method is presented for splitting the coupled signal of the tilt sensor into two parts: the inclination angle signal and the vibration signal. The inclination angle signals can be converted to distributed horizontal deformation through a cumulative algorithm. And the vibration intensity can be inferred from the vibration signal. The measuring principle, structure design, and calibration experiment of the inclinometer were present in detail. A distributed horizontal deformation generating device with high precision was specially developed to simulate the internal deformation of slope. Verification experiments further validated the feasibility of the proposed inclinometer for simultaneous measurement of horizontal deformation and vibration induced by sudden deformation.