The Eu2+/3+ mixed-valent complexes have aroused attention because of their potential application in the catalytic field endowed by the variable valence. Herein, we develop an ingenious green strategy to achieve the partial reduction of Eu3+ to Eu2+ ions in the complex of pyrenol-containing cyclen (H-4(Pyr)(4)cyclen, H-4[PC]) via a ligand-to-metal charge transfer (LMCT) effect in air at room temperature. To reveal the inherent regulated capacity of the Eu2+/3+ complex in catalysis, we prepared the nanocomposites assembled by the lanthanide complexes encapsulated into ZIF-67 to successively realize the decomposition of H2O2, including europium, gadolinium, and terbium complexes. Among the nanocomposites, Eu2+/3+[PC]H@ZIF-67 exhibits the best catalytic performance due to the achievement of dual regulation of Co3+/Co2+ ratio by the mixed-valent complex. Because of extremely abundant Co2+ active sites, the Eu2+/3+[PC]H@ZIF-67 after catalyzing H2O2 sample was further utilized to degrade organic dye rhodamine B (RhB). The rather outstanding catalytic degradation efficiency was still present in Eu2+/3+[PC]H@ZIF-67. This research presents a facile strategy of Eu3+ reduction based on the ligand design and a new direction for the future development of the composite catalytic materials with mixed-valent complexes.