In this work, a novel effective heterogeneous catalyst metal-organic framework MIL-53(Fe) has been synthesized for the purpose of activating persulfate (PS). Catalytic performance of MIL-53(Fe) activated under different vacuum conditions was investigated; stability and reusability of the catalyst were evaluated, and the activation mechanism was also investigated. The results indicated that vacuum activation could cause variation of the FeII/FeIII relative amount ratio of the catalyst, and thus would change the catalytic activities of MIL-53(Fe), because FeII or FeIII CUS (coordinative unsaturated metal site) are alternative active sites. It was found that MIL-53(Fe)-2 exhibits good performance for PS activation and could be used for multiple cycles. A removal rate of 98% for Orange G was obtained within 120min (95.7% mineralization efficiency), and 94.3% was attained in the fifth cycle. The mechanism of the activation of PS by MIL-53(Fe) was also suggested, which involves a predominant heterogeneous reaction and an auxiliary homogeneous reaction. The findings of this study provide new insight into the application of the reactive metal-organic frameworks in activating persulfate for the degradation of environmental contaminants.