The availability of soil nutrients, e.g. phosphorus (P) and potassium (K), and their spatial distribution are key factors controlling plant growth, community development, and ecosystem restoration. Karst is one of the main fragile habitat zones in China. In this study, we examined the soil P and K and their spatial heterogeneity in a 500 m×500 m long-term monitoring forest plot in the Mulun National Nature Reserve, Guangxi, using classical statistics and geostatistics methods. The results showed that the average contents of total phosphorus (TP), total potassium (TK), available phosphorus (AP), and available potassium (AK) in the studied area were (1.60 ±0.76) g/kg, (5.42 ±2.74) g/kg, (5.74 ±3.63) mg/kg, and (5.20 ±2.96) mg/kg, respectively. The variability of soil P and K at a moderate intensity level, and the order of which was AP > AK > TK > TP. Exponential model was best-fitted for the semivariogram of soil TP, TK, AP and AK, and the coefficients of determination are very high, ranging from 0.671 to 0.995. The contents of TP and AP showed moderate spatial autocorrelation, which indicated that the variations were caused by structural variation and random factors, whereas TK and AK had weak spatial autocorrelation. TP and AP had a relatively long autocorrelation distance (336.00 m and 373.50 m, respectively), indicating a relatively good spatial continuity. The autocorrelation distances of TK and AK (33.30 m and 64.50 m, respectively) were shorter than those of TP and AP, suggesting a strong spatial dependence. The distribution of TP in the soil was high on the toe slope (including depressions) and low on the upslope. AK content was higher on the slope than in depression. In addition, both AP and TK had patchy distributions. Elevation, slope, and convex topography were the main factors determining the spatial heterogeneity of soil P and K. Overall, soil P and K showed different patterns for spatial heterogeneity and spatial correlation in karst mixed evergreen and deciduous broad-leaved forest, which provides a reference for site-specific soil nutrients management and designing strategies for ecological restoration of degraded ecosystems in the karst region.