The key to reducing the environmental and human health hazards of heavy metals is to choose proper washing agents to remediate heavy metal-contaminated soil. In this study, ferric nitrate and citric acid (CA) were used to remove Cu, Zn, Pb, and Cd from contaminated soil. The effects of concentration, liquid-solid ratio, and time of the washing processes were investigated. Besides, the effects of ferric nitrate or CA on soil fertility and the potential ecological risk of heavy metals after soil washing were also studied. In ferric nitrate remediation, the optimal removal efficiencies of Cu, Zn, Pb, and Cd were 78.68%, 58.96%, 48.53%, and 80.86%, respectively. On the contrary, in CA remediation, the optimal removal efficiencies of Cu, Zn, Pb, and Cd were 66.59%, 43.10%, 37.95%, and 77.48%, respectively. The washing with both ferric nitrate and CA significantly reduced the potential ecological risk of heavy metals in the soil, whereas ferric nitrate showed better performance in lowering the metal risks than CA. Soil properties had been improved to some extent, including invertase activity, acid phosphatase activity, available phosphorus, and available nitrogen. The washing results showed that ferric nitrate exhibited better performance than CA. This study suggests that ferric nitrate can be considered a suitable agent for washing soil contaminated by heavy metals.