The advanced oxidation processes (AOPs) with Fe(II) as homogenous activator suffer from the accumulation of insoluble Fe(III) oxides which results in the decrease of available catalyst and increase of iron sludge. Herein, with Fe(II)/peroxydisulfate (Fe(II)/PDS) process as an example, HSO was proposed to enhance the regeneration of Fe(II). The results showed that 250 µM of HSO increased the removal of benzoic acid (BA) from 18.8% to 41.3% while further increasing HSO dosage promoted its scavenging effects and decreased BA removal. Accordingly, multiple-dosing mode of HSO was used which enhanced BA removal to 63.8%. Addition of HSO recovered Fe(II) from Fe(III)/Fe(IV) and shifted the distribution of reactive species from Fe(IV) to SO. Besides as the reductant, the reaction of HSO with Fe(III) and Fe(IV) severed as the AOPs and produced SO. A mathematic model was constructed for the Fe(II)/PDS/HSO process, and it revealed that ∼ 78% of dosed HSO was transformed to SO, but ∼ 81% of the generated SO was consumed by HSO. The reaction of Fe(IV) with HSO and the activation of in situ formed peroxymonosulfate by Fe(II) are chiefly responsible for SO formation with the contributions of ∼ 47% and ∼ 27%, respectively, in the Fe(II)/PDS/HSO process. Considering the complexity of the multiple-dosing mode of HSO in the real practice, the sparingly soluble CaSO which released HSO gradually was synthesized and used. The single dosing of CaSO stood out in terms of promoting pollutant abatement by the Fe(II)/PDS process compared to that adding equivalent of HSO. These results will benefit the optimization of the Fe(II)-based AOPs.