Soil acid buffering capacity governs the sensitivity of its pH to external acid inputs, yet the relationships between buffering capacity and fundamental physicochemical properties, as well as their regional-scale variability, remain insufficiently understood in tropical acidic soils. To address this gap, 42 representative surface soil samples were collected across Hainan Province. By measuring soil pH buffer capacity (pHBC), basic chemical properties, surface site concentration, and mineral composition, and combining correlation analysis, regression modeling, and geostatistical methods, this research reveals the current status, dominant influencing factors, and spatial distribution of soil acid buffering capacity in Hainan. The results revealed that the pHBC in Hainan ranged from 14 to 30 mmol/(kg pH), with an average of 21.47 ± 0.68 mmol/(kg pH), indicating an overall weak buffering capability. No significant relationship was observed between pHBC and soil pH. Instead, pHBC was primarily co-regulated by soil organic matter (SOM) and cation exchange capacity (CEC)(pHBC= 10.271 + 0.461CEC + 0.333SOM, R2 = 0.536, P< 0.001), which together explained 53.6% of the variation in pHBC, with SOM contributing more strongly. Mineralogical analysis indicated that Latosols (the typical soil in Hainan) are primarily composed of kaolinite and iron/aluminum oxides, which provide limited reactive surface sites, representing the intrinsic reason for their low buffering capacity. Spatially, pHBC exhibited a pattern of "higher in the northeast and central regions, lower in the southeast and southwest coastal areas," which closely mirrored the spatial distribution of SOM and CEC. This study suggests that enhancing SOM and CEC is the key to improving acid resistance in highly weathered tropical soils, thereby providing a scientific basis for the zonal management and targeted remediation of acidic soils in Hainan and similar tropical regions.