The internal displacement sensor is an automated monitoring sensor for three-dimensional spatial deformation in geotechnical engineering. It represents a novel, intelligent three-dimensional deformation monitoring sensor system adaptable to various industry applications. It is designed for comprehensive displacement measurement in three-dimensional space and is suitable for applications such as deep-seated slope displacement monitoring, tunnel convergence deformation monitoring, and deep foundation pit inclinometry. The sensor completes data acquisition and calculation, directly outputting the coordinates of the monitoring point without the need for external data processing. Additionally, it can optionally output multi-source collaborative monitoring indicators such as angle and temperature.