This study examines the distribution of heavy metals in the agricultural soil of the Longchuan River basin, situated in central Yunnan.Methods: A concentrated farmland area in Chuxiong City, Yunnan Province was selected as the study site, and topsoil samples (0~20 cm) were systematically collected. The analysis encompassed evaluations of soil pH and the concentrations of eight heavy metals: arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn). To assess the risk of heavy metal pollution, the study employed soil pollution risk screening values for agricultural land as a reference point, utilizing both the Nemerow Comprehensive Pollution Index and the Potential Ecological Risk Index methodologies. These approaches facilitated the assessment of pollution risk, identification of primary sources of heavy metal contaminants.Results: The overall soil environmental quality was good, with an average pH of 6.78 (neutral). Except for localized Cd exceedances along the Longchuan River banks, heavy metal pollution risk was generally low. Compared to Yunnan soil background values, As, Pb, Hg, and Zn were depleted; Cr, Ni, and Cu were similar; Cd was relatively enriched. The average Nemerow composite pollution index was 0.616, and the average comprehensive potential ecological risk index was 32.54, indicating overall low heavy metal hazard but notable local ecological risk from Cd.Conclusions: PMF analysis revealed five principal sources: pedogenic parent material weathering (natural source, 29.65%), atmospheric deposition (23.33%), a mixed source of agricultural activities and riverine sedimentation (17.75%), direct agricultural activities (17.54%), and a mineralized stratum source associated with mining activities (11.74%). The results underscore the combined influence of natural geology and human activities on soil heavy metal accumulation in this high- background area.