To overcome at the limitations of traditional electronic monitoring methods in geophysical observations, this study develops a fiber optic inclinometer system based on a Fabry-P-rot (F-P) interferometric cavity. The system combines a vertical pendulum mechanism with dual F-P interferometric cavities, using differential measurement techniques to effectively suppress environmental noise and temperature drift. The interferometric optical path and phase demodulation algorithm are optimized to significantly enhance the precision of tilt angle detection. Experimental results demonstrated that the system achieves a tilt sensitivity of 2 435 nm/″ and a resolution of 0.000 078 ″ within a measurement range of -181.6″ to 181.6″, showing excellent precision and stability. Continuous monitoring experiments conducted at the Tai′an Seismic Monitoring Center Station successfully recorded periodic solid earth tide variations, with the waveforms closely matching those observed by a VP-type electronic inclinometer, confirming the system′s high resolution and low drift characteristics. Furthermore, multiple seismic events were captured during the experiment, demonstrating the feasibility of simultaneous monitoring of solid earth tides and seismic activity. In comparison with the traditional VP-type electronic inclinometer, the fiber optic inclinometer not only accurately recorded standard seismic signals but also detected small seismic signals, indicating a clear advantage in terms of sensitivity and noise suppression. This fiber optic inclinometer system provides a new tool for crustal deformation measurement and seismic observation, with high resolution and sensitivity that meet seismic industry standards. The experimental results show that the system can effectively monitor solid earth tide waveforms and seismic events, demonstrating significant potential for widespread application. This technology provides a reliable basis for earthquake monitoring and crustal dynamics research and is expected to contribute to innovations in future geophysical observation equipment.