Forest soil organic carbon (SOC) is the main component of the terrestrial carbon reservoir, and plays a crucial role in the Earth's carbon cycle. This study aimed to quantify the spatial heterogeneity and distribution patterns of SOC density. The study was conducted in a 60 hm² forest plot in a tropical mountain rainforest of Jianfengling, Hainan Island, China, using field investigation, laboratory analysis, and geostatistical methods. The results showed that the mean SOC density at different soil profile depths (A [0-10 cm], B [10-30 cm], and C [30-60 cm]) was 2.699, 2.782, 2.434 kg/m², respectively. The differences for A versus C and, B versus C layers were statistically significant (P < 0.05), but there was no significant difference between A and B layers (P > 0.05). Cross-validation results showed that the most fitted models for SOC density at different layers was exponential for A and spherical for B and C. The ranges of SOC density were 54.2 m, 70.9 m, and 97.2 m for A, B, and C, respectively, while the Nugget:Sill ratios were 0.512, 0.708, and 0.882, respectively. This result implies that SOC density is moderately variable for A and B, but weakly variable for C. Thus, SOC had more significant spatial variability at the small scale.Pearson correlation analysis showed that the correlation coefficients for A versus C and B versus C were less than that between B and C, indicating that different ecological processes may regulate SOC density across surface and subsurface soil layers. Ordinary Kriging interpolation showed that A and B soil layers had moderate spatial autocorrelation, whereas the C layer had weak spatial autocorrelation. Meanwhile, the contour maps produced scattered spatial distributions for the A and B layers, but a banded distribution for the C layer. Topography-induced water and heat distribution may represent an important factor affecting the spatial distribution patterns of SOC density in different soil layers.