In recent years, ecological restoration techniques for rocky slopes have been widely applied. However, the substrate-rock interface formed during restoration acts as a potential weak plane, and its moisture evolution characteristics remain insufficiently understood. This study focuses on an ecologically restored bare rocky slope in a historical mining area in Dali Bai Autonomous Prefecture, Yunnan, China. The region has a subtropical monsoon climate with distinct dry and wet seasons, providing ideal conditions to study seasonal moisture dynamics at the interface. Field monitoring of meteorological and hydrological data, wavelet coherence analysis (WCA), time-series analysis (TSA), and partial least squares structural equation modeling (PLS-SEM) were integrated to reveal spatiotemporal moisture evolution at the interface under three substrate covers: laterite, humus, and Phaeozem. Results indicate pronounced spatiotemporal variability in shallow slope moisture. During seasonal transitions, humus exhibited the strongest moisture response (CV=46.63). The interface layer displayed clear water-storage and infiltration-retarding functions, with the laterite interface showing the highest water-retention capacity (Delta theta 2,r = 32.37); however, moisture accumulation weakened interlayer connectivity, with correlations decreasing to 0.3390 and 0.3763. The responses of moisture dynamics and connectivity to rainfall intensity are regulated by substrate permeability, resulting in distinct positive or negative correlations. In terms of applicability, Phaeozem is suitable for long-term restoration in humid regions, laterite short-term projects in arid regions, and humus short-term restoration in regions with weak seasonal variability. This study clarifies hydrological differences among substrates from an interface perspective and provides criteria for optimizing substrate configuration under complex climatic conditions.