Abstract: The Lishi Formation loess, buried deeply beneath the phreatic water-rich aquifer in the Quaternary sand layer within the Jinjitan Mining Area, serves as a crucial aquiclude widely distributed in the region, and its engineering geological properties are of double-significant importances for mine safety and regional ecological environment protection. This paper systematically investigates the mineral composition, grain size composition, microstructure, and physical-hydraulic-mechanical properties and their relevance of the Lishi Formation loess, utilizing an X-ray diffraction test, scanning electron microscope test, conventional geotechnical test, and triaxial consolidation and drainage shear test, to reveal its engineering geological properties. The results demonstrate that the mineral composition of the Lishi Formation loess is predominantly quartz and clay minerals, with the clay minerals primarily consisting of illite and illite/montmorillonite mixed-layer. The grain size composition is mostly comprised of silt particles, followed by sand particles and clay particles; the structural type exhibits a flocculation structure with well-developed intergranular pores. The Lishi Formation loess is characterized by high saturation, low liquid limit, micro to moderate water permeability, and low-medium compressibility, existing in varying states of slightly wet-wet, dense, and hard-hard plastic-plastic. The stress-strain curves of undisturbed loess exhibit strain-hardening, transitioning from weak to strong strain-hardening type with increasing confining pressure. The content of clay particles has a significant positive correlation with the liquid limit, plasticity limit, and cohesion, while showing a significant negative correlation with compression modulus; significant negative correlations are found between cohesion and both the water content and saturation. The Lishi Formation loess possesses a certain water stability and structural strength, and its water resistance and shear strength increase with increasing buried depth. The study results can provide scientific references for mine safety production and regional ecological environment protection.