In this study, LaCoO3/Al2O3 (LCA) was utilized as a heterogeneous catalyst to activate peroxymonosulfate (PMS) to degrade atrazine (ATZ). The structural properties of the catalysts were characterized by SEM, EDS, XRD, XPS and TPD. The effects of some key parameters (i.e., loadings of LCA, ATZ concentration, catalyst dosage, PMS concentration, initial pH and coexisting ions) were optimized. In addition, under the optimal conditions of 100 mg/L 23LCA, 100 mg/L PMS and initial solution pH 6.8, the removal rate and mineralization efficiency of ATZ (5 mg/L) reached 100% and 30.8%, respectively. The superiority of the 23LCA/PMS system was verified by two controlled experiments. After three cycles of experiments, the degradation effect of ATZ was within an acceptable range. The degradation intermediates of ATZ were detected by UPLC-QTOF-MS/MS, and the possible degradation pathway of ATZ was proposed. In addition, the presence of SO4 center dot- and HO center dot was identified by quenching experiments and SO4 center dot- was verified as the predominant radical. Finally, based on the comprehensive analysis, a reasonable reaction mechanism of the 23LCA/PMS system was proposed. In a word, these results indicate that LCA can act as a highly efficient heterogeneous catalyst to activate PMS to degrade ATZ in water.