Objective This study aims to investigate the co-developmental relationship between the overlying soil and the underlying strongly weathered bedrock layer， thereby providing fundamental data for the quantitative prediction of subsurface rock-soil structures in karst areas. Methods In the Mulian small watershed of Huanjiang， Guangxi， intelligent photogrammetry technology was employed， using a 3 m high standard leveling staff as a reference， to investigate 68 rock-soil profiles， each 5 m in width， across four different geomorphic positions： upper slope， middle slope， lower slope， and depression （17 profiles per position）. Through image characterization in AutoCAD and vectorization processing using ArcGIS-Fragstats， structural indicators of the rock-soil profiles were obtained and compared， including equivalent thickness （T）， number of patches （NP）， shape index （SHAPE）， perimeter-to-thickness ratio （PTR）， fractal dimension （FRAC）， and coefficient of variation of thickness （CV）. Results 1） The equivalent thickness of the soil layer and the strongly weathered bedrock layer increased non-uniformly from the upper slope to the depression. The soil thickness on the upper slope was less than 25 cm， while the thickness of the strongly weathered bedrock layer in the depression ranged from 110 cm to 250 cm. 2） The number of patches （NP>4） and the shape index （SHAPE） on the middle slope were significantly higher than those at other slope positions， exhibiting fragmented and interlocked rock-soil mosaic characteristics. The number of trees and shrubs and the maximum root depth were significantly positively correlated with the thickness of the soil and the strongly weathered bedrock layer （r=0.86， r=0.65）， and increasing woody vegetation effectively reduced the spatial variability of soil thickness. 3） A linear model indicated that the thickness of the strongly weathered bedrock layer was approximately 69% of the soil layer thickness. The complex characteristics of the concealed subsurface structure could be effectively predicted through easily measurable surface indicators， such as soil thickness （T） and woody stem density （Sd）. Conclusion Quantitative research at the rock-soil profile scale reveals differences in structural characteristics among various geomorphic positions， providing a scientific basis for precise zonal management of geomorphic positions in karst ecological restoration.