The displacement monitoring of the slow landslide deep deformation is an important part of the landslide early warning system. However, the traditional energy supply mode of depth sensors limits the large-scale landslide monitoring of the whole life cycle. Therefore, it is necessary to realize self-powered monitoring for deep deformation at extremely low speed. Herein, an extremely low-speed triboelectric tilt sensor (ELS-TTS) is proposed for whole life cycle monitoring of landslide deep deformation without an energy supply. The triboelectric self-sensing unit based on the triboelectric nanogenerator (TENG) and the instantaneous structure of gravity energy storage is designed. A prototype of ELS-TTS with a resolution of 0.075° is fabricated and experimented. ELS-TTS can stably monitor extremely low speeds of below 0.0257° s−1 in different environments and motion states, and the monitoring error is less than 0.13°. Furthermore, a real-time monitoring system for deep landslides based on a multi-level forewarning method is proposed to realize the whole life cycle monitoring of landslides and the multi-level forewarning of dangerous states. This work further promotes the development of TENG in the fields of natural disaster prevention and structural health monitoring.