Abstract: Chelated ferrous is representative of highly efficient activators of persulfates for the removal of organic contaminants in soils. However, chelated ferrous-activated persulfate systems suffer from the low utilization efficiency of remediation reagents, due to the well-known competition of natural soil components (e.g., organic matter and reductive minerals) for the reactive substances. In this study, we chosen citric acid-chelated ferrous (Fe^2%2B-CA) as a model activator of persulfates, and investigated effects of Fe^2%2B-CA addition in advance on remediation performance and utilization efficiency of Fe^2%2B-CA/PS for the removal of organic pollutants in soils. Results showed that adding Fe^2%2B-CA in advance by 0-120 min to different extents influenced the degradation rates of pesticide atrazine in soils by Fe^2%2B-CA/PS, characterized by an inverse U type curve of activator addition interval (min). The maximal removal rate of atrazine (73.6%) was achieved in soils by Fe^2%2B-CA/PS, when the activator was added in advance by 5 min. This removal rate was about 17% higher than that by Fe^2%2B-CA/PS into which both activators and oxidants are simultaneously added. In the soils treated by Fe^2%2B-CA/PS, where the activator was added in advance by 5 min, much sulfate radicals were generated as main reactive substances, and the losses of soil organic matter and persulfates were decreased. These impacts resulted in both improvement of atrazine removal and utilization efficiency of persulfates in soils. This phenomenon was obtained in various Fe^2%2B-CA/PS systems, despite large differences in oxidant doses and soil types as well as chemical diversities of organic contaminants. Pilot soil remediation experiments demonstrated the performance of Fe^2%2B-CA/PS with activator addition in advance by 5 min, and the removal rate of atrazine in soils (approximately 80% of the maximal holding capacity of water) was increased by 47%. This finding may provide a technical basis for the application of Fe^2%2B-CA/PS in soil remediation contaminated by various organic pollutants.