Abstract: Basic farmland plays an important role in grain quality and security. Research on the potential ecological risk of farmland top-soil of heavy metals is of great guiding significance for increasing grain yield and security. Based on the assessment standard of the soil quality geo-chemical survey, this article selects the basic farmland in Nanling county in Anhui as the main study area, and a total of 500 top-soil samples (depth of 0~20 cm) are collected. By using the methods of geo-accumulation index and potential ecological risk index, the potential effects of heavy metals in the top-soil of Nanling farmland are examined. The results show that (1) there is no pollution of the heavy metal element Cr in the top-soil, however, the rest of heavy metals occur harmful effects in varying degrees; (2) the contents of heavy metals Cd, Hg and Fe exist regional abnormal in top-soil and mean concentration of these heavy metals are more than the geo-chemical background value of Nanling county 1.92, 1.95 and 7.13 times, respectively, which carries potential risk for the grain quality and security; (3) the mean RI value is 164.5, indicating that the Nanling farmland sufferes from a moderate-level potential ecological risk and the principle heavy metals element are Cd and Hg.