This work delivered a simple modification method for promoting persulfate (PS) activation by zero-valent iron (ZVI). The results showed that the ball-milled FeS/Fe0 had the highest imidacloprid (IMI) removal efficiency among the tested materials (FeS, Fe0, mixed FeS/Fe0, and ball-milled FeS/Fe0) under the same conditions (activator dosage = 0.1 g/L; PS = 2.5 mM; IMI = 0.15 mM). Ball milling ZVI and FeS together makes the mixture smaller in particle size, higher in crystallinity and produces iron-sulfur compounds that covered the surface. These changes contributed to the rapid corrosion of ZVI and thereby promoted the persulfate activation. Increasing the ball milling rotational speed made these enhancements more obvious. In addition, the Fe3+ reduction by FeS created an acidic condition and further promoted the Fe0 release. The optimal parameters for ball milling FeS and Fe0 were a FeS/Fe0 (1:1–4:1, w:w) and a 600 rpm of rotational speed for 30 min. The impacts of different ball-milled material dosages, persulfate dosages, anion concentrations and initial pH were investigated. In the optimum ball-milled FeS/Fe0/PS system (ball-milled FeS/Fe0 = 0.1 g/L; PS = 2.5 mM), the pollutant (IMI = 0.15 mM) removal efficiency reached 95% at 10 min. The common dissolved anions (3 mM SO42−/NO3−/Cl−) and alkaline conditions only had a slight inhibitory effect. The IMI removal efficiency still reached 95% at 15 min. These observations suggest that the Fe0-based persulfate activation technique was enhanced by ball milling with FeS, making it more feasible for remediation of organic pollutant removal.