The Jiulong-Fenggang area on the south shore of Poyang Lake was selected as the study area to identify the pollution risks and sources of heavy metals in the soil within the Poyang Lake embankment region. A total of 3,799 topsoil samples and 26 soil profile samples were collected. The pollution status was assessed using three methods: the geoaccumulation index, the Nemerow index, and the potential ecological risk index. The positive definite matrix factor decomposition method (PMF) was employed to analyze the sources of heavy metals in the soil. The results indicated that the average concentrations of As, Cd, Cu, Cr, Hg, Ni, Pb, and Zn in the surface soil of the embankment area were 1.06 to 2.10 times higher than the background values of the soil in Jiangxi Province. The geoaccumulation index revealed a non-polluting to slightly polluting level. The comprehensive potential ecological risk index indicated primarily a low-risk level. The comprehensive Nemerow index suggested that the area was mainly non-polluted, with only the sampling sites in the tidal flats showing moderate to high levels of pollution, where Cd was the primary contributor. Due to the influence of the upstream water system, the concentrations of heavy metals, particularly Cd, in the vertical profile soil and surface soil in the tidal flats outside the embankment area were significantly elevated, exceeding the standards, while the heavy metal concentrations in the soil within the embankment area remained relatively stable. Joint analysis identified four sources of heavy metals in the soil: secondary enrichment during red soil formation (49.28%), upstream industrial and mining activities (20.19%), weathering of parent rocks in coal-bearing strata and agricultural production (11.91%), and coal combustion (18.62%). Notably, soil Cd primarily originated from upstream transport (79.92%), providing an effective basis for the precise prevention and control of heavy metal pollution in farmland within embankment areas and ensuring safe utilization.