A novel phosphovanadomolybdate-based ionic polymer/Fe3O4 composite catalyst Fe3O4@PIL-PMoV was synthesized, and fully characterized by FT-IR, TG, XRD, SEM, and VSM. Its catalytic performance was investigated in the hydroxylation of benzene to phenol with H2O2. The results demonstrate that Fe3O4@PIL-PMoV is a highly efficient heterogeneous solid catalyst for hydroxylation of benzene using CH3CN as the solvent, and the phenol yield and selectivity were 24.5% and 100%, respectively. After reaction, the catalyst could be easily recovered by an external magnet and reused directly in the next run. The excellent catalytic performance of the catalyst are closely related to the “solvent role” of the functional –COOH groups and the “pseudo-liquid behavior” of the heteropolyanion.