Urbanization profoundly influences the synergistic relationship between vegetation and soil in urban remnant natural mountain ecosystems, but its coupling response mechanism is not clear. In this study, the urban remnant natural mountains in the karst region were selected as the research object, and 12 mountains were selected along the urbanization gradient (high, medium and low intensity). We established an evaluation system based on 9 vegetation and 10 soil factors derived from vegetation community surveys and soil physicochemical analyses. Using a combination of the analytic hierarchy process and the entropy weight method to determine factor weights, we constructed a Coupling Coordination Degree Model (CCDM) to systematically analyze how urbanization influences vegetation characteristics, soil properties, and their interaction. The results showed that: (1) Simpson index and Richness index of plant species diversity decreased gradually with the increase of urbanization intensity; the FRic, FDis and Rao'Q indexes of functional diversity were significantly different under different urbanization intensities, showing a pattern of medium urbanization>low urbanization>high urbanization. The stability of plant communities decreased significantly from low to high urbanization areas, showing significant spatial differentiation. (2) Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), alkali-hydrolyzable nitrogen (AN) and available potassium (AK) showed significant differences under different urbanization intensities, available potassium was enriched in high urbanized areas, while total nitrogen and alkali-hydrolyzable nitrogen were significantly higher in low urbanized areas. (3) The vegetation-soil coupling coordination degree of urban remnant natural mountains changed with urbanization intensity, but all of them were in a state of reluctant coordination. The highest coupling coordination degree was under low urbanization intensity (D_c=0.589), followed by high urbanization area (D_c = 0.532). The middle urbanization area showed a significant imbalance due to the lag of soil quality (P(y)/S(x)=2.516), and the coupling coordination degree was the lowest (D_c = 0.503). Urbanization weakens the vegetation-soil coupling relationship by changing habitat heterogeneity and nutrient cycling. Ecological restoration strategies need to be optimized based on gradient differences: low-urbanization areas need to protect natural habitats, medium-urbanization areas should improve soil nutrients to balance system development, and high-urbanization areas need to introduce deep-rooted plants to alleviate soil degradation. The results provide a reference for further revealing the impact of urbanization on the interaction between plant communities and soil properties in the urban remnant natural mountains, and provide theoretical support for ecological protection and sustainable planning of multi-mountainous city in the karst region.