In order to reasonably assess the risk of contaminated sites, the total amount of Cu, Pb, Cd, and As heavy metals in the soil was determined by taking the farmland soil downstream of a copper pile leaching site in Yunnan, China as an example. The occurrence forms of the four heavy metals were determined by improved BCR (Bureau of European Communities Reference) continuous extraction method, and the correlation among the four heavy metals was analyzed. The soil heavy metal pollution and potential risk were evaluated by in-situ accumulation index (I_geo), primary and secondary comparison value (RSP) and the risk assessment coding method (RAC). The results show that the average contents of Cu, Pb, Cd, and As are 39.50, 46.98, 0.16, and 82.67 mg·kg^-1. Compared with the background value of heavy metals in Yunnan, the over-standard rates of the four heavy metals are 0%, 83.33%, 33.33%, and 100%, among which the pollution of As required special attention. The results of heavy metal occurrence indicate that Cu, Pb, Cd, and As are mainly in residual form, accounting for 83.14% to 95.62%, suggesting that the four heavy metals exist in stable form in soil. A comparison of the four evaluation methods demonstrates that there are significant differences in evaluation results. The I_geo results show that only As pollution exceeds the standard, while the other three heavy metals are pollution-free. The RSP results show that the four heavy metals are pollution-free to the environment. The RAC results show that Cd has a low risk to the soil environment, while the other three heavy metals had no risk. By comparison, it is found that only the total amount of heavy metals in the soil of the polluted site as an evaluation index would exaggerate the pollution risk to a certain extent, and the analysis should be conducted by combining the total amount of heavy metals and the content of their occurrence forms. Although the total concentration of heavy metal pollutants is relatively high, the content of a bioavailable heavy metal is very low, resulting in a minimal risk of diffusion into the environment. Therefore, the study area is subject to mild heavy metal contamination, with a low level of potential ecological risk.