In view of the frequent detection of atrazine (ATZ) in water body, which is a recalcitrant herbicide, zero-valent iron activated peroxymonosulfate (PMS/Fe⁰) was proposed to remove the ATZ in water. The effects of operation parameters (pH value, initial ATZ concentration, and PMS and Fe⁰ dosages) on ATZ degradation were investigated. Then the reactive species in PMS/Fe⁰ system were in-situ identified based on the competitive reactions of nitrobenzene (NB) and ATZ, and the formula for radical production ratio was derived under steady-state assumption. Finally, the degradation of ATZ by PMS/Fe⁰ was investigated under simulated groundwater condition. Results show that the pseudo-first order rate constant (k_obs) of ATZ degradation decreased with increasing pH value and initial ATZ concentration, and increased with increasing Fe⁰ dosage. While it increased first and then decreased as the PMS dosage increased, reached the maximum at 25 μmol/L PMS. The competition experiment shows that sulfate radical (SO-₄·) and hydroxyl radical (·OH) were reactive species in PMS/Fe⁰ system, and the production ratio of the two radicals was calculated to be 10.5∶1. ATZ degradation efficiency could reach 87% at 0.25 g/L Fe⁰ and 25 μmol/L PMS under simulated groundwater condition, indicating the prospective performance of PMS/Fe⁰ under groundwater conditions. The research results can provide theoretical reference for PMS/Fe⁰ applications in remediation of atrazine-polluted groundwater.