This study investigated the removal performance and synergistic mechanism of p-arsanilic acid (p-ASA) using a pre-oxidative coagulation system of potassium permanganate (K2FeO4) with aluminum chloride (AlCl3) or ferric chloride (FeCl3). The arsenic removal efficiencies of K2FeO4-AlCl3 and K2FeO4-FeCl3 reached 93.46% and 98.58%, respectively. K2FeO4 could alter the distribution of hydrolysis products of the coagulants and the addition of the coagulants directly or indirectly influenced the generation of intermediate valence iron (Fe(IV) and Fe(V)), interestingly, the mechanisms of aluminum and iron salts enhancing the removal of p-ASA by potassium ferrate were different. During the coupling process, AlCl3 and FeCl3 enhanced the self-decomposition rate of K2FeO4 with △kAl = 3.0530 and △kFe = 0.0912, respectively, resulting in difference on the generation of Fe(IV) and Fe(V). FeCl3 facilitated more effective Fe(IV) and Fe(V) production (FeCl3eff/AlCl3eff>1), and multiple active iron species degraded p-ASA into inorganic arsenic, p-aminophenol (p-AP), nitarsone (NIA), and other products. Additionally, in the presence of K2FeO4, the hydrolytic dominant species of AlCl3 and FeCl3 were influenced under near-neutral conditions (pH 6–8), and Al13 and polynuclear Fe-hydroxides (PnFe-H) effectively improved the removal efficiency of inorganic arsenic and other organic products. The in-situ generation of nanoiron particles by K2FeO4 altered the original floc structure of the coagulants, with the specific surface areas of the flocs being 8733.176 cm2/cm3 for K2FeO4-AlCl3 and 7232.856 cm2/cm3 for K2FeO4-FeCl3. The coupling of K2FeO4 with metal salt coagulants not only enhanced p-ASA removal but also effectively improved the floc structure.