［Purposes］ This work aims to evaluate the leaching behavior and potential ecological risk of heavy metals of steel slag that was stacked or used as a subgrade backfill.［Methods］ The leaching behavior and mass concentration of heavy metals (Fe, Mn, Zn, Cu, and Cr) of steel slag from Jiangxi Pinggang with three particle sizes were studied by the long-term leaching test method, which was soaked in three leaching agents of pH = 3.2, 4.2 and 7.0; Subsequently, the potential risk coefficient was calculated.［Findings］ A smaller pH of the leaching agent and the particle size of the steel slag resulted in a greater mass concentration of heavy metals in the leaching solution, the mass concentration of Fe reached the peak at 14 days, and that of Mn, Zn, Cu, and Cr increased with the extension of soaking time; The mass concentration of heavy metals in steel slag rarely exceeded the limit specified in reference ［19］, whereas it exceeded the limit specified the standard for Class I surface water in the leaching agent with pH=32 and pH=42.［Conclusions］ The steel slag of Pinggang is not a hazardous waste with leaching toxicity characteristics, but the leaching solution of steel slag exhibited the potential ecological risk of heavy metal pollution to the surrounding water resources.