Perovskite oxides are promising catalysts in peroxymonosulfate (PMS) activation for wastewater treatment, attributed to their flexible structures. In this study, halogen anion (F− or Cl−) was doped in La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) for PMS activation, showing that appropriate anion doping enhances the catalytic performances. La0.6Sr0.4Co0.8Fe0.2O2.75-δCl0.25 (LSCFCl0.25) exhibits a superior catalytic activity to pristine LSCF and La0.6Sr0.4Co0.8Fe0.2O2.75-δF0.25 (LSCFF0.25), attributed to the strong surface acidity, sufficient oxygen vacancies, and improved B-site metal−oxygen bonding. The rich acidic sites favor PMS adsorption on the catalyst surface. The sufficient hydrated electrons (eaq−) in the oxygen vacancies participated in the generation of free radicals (SO4•− and O2•−) and singlet oxygen (1O2). The enlarged B-site metal−oxygen covalency could boost the electron transfer between PMS and Co(III)/Fe(III), and thus accelerate the redox reaction. SO4•− and 1O2 are the dominating species for the degradation. This study deepens the catalytic mechanism and uncovers the active sites of perovskite catalysts for PMS activation, providing an inspiring modification strategy to improve the catalytic performances. Display omitted •Anion doping improves the catalytic activity of La0.6Sr0.4Co0.8Fe0.2O3-δ.•Electrons in the oxygen vacancy favor the generation of ROS.•Enlarged B-site metal-oxygen covalency improves the redox capability of catalysts.