Engineering biocompatible hydrogels using functional nanoparticles has attracted considerable attention because of their uniquely appealing cooperative effects that can enable multimodality imaging and treatment with improved efficacy against serious diseases. However, the effects of high‐content nanoparticle dopants on the rheological properties of hydrogels frequently lead to an unsatisfactory therapeutic result, which is particularly notable in the design of magnetic hydrogel formulations for cancer therapy. Herein is reported a novel magnetic hydrogel functionalized by ferromagnetic vortex‐domain iron oxide (FVIOs) with optimally adaptive functions for prevention of breast cancer recurrence. The FVIOs can perfectly incorporate into the dynamic hydrogel networks with an extremely low concentration (0.6 mg mL−1), 17 times lower than that of conventional superparamagnetic iron oxide nanoparticles with sufficient heating capacity. Such magnetic hydrogels exhibit high inductive heating and remarkable rheological properties simultaneously. Moreover, the self‐healing, self‐conformal ability, controlled release of loaded doxorubicin, biodegradation, and pH‐responsiveness of the magnetic hydrogel project their efficient sustainable therapeutic ability. In vivo postoperative treatment has further demonstrated the high efficacy of FVIO‐based magnetic hydrogels, as evidenced by the significant suppression of the local tumor recurrences compared to chemotherapy or hyperthermia alone. This unique magnetic hydrogel formulation with optimally adaptive functions shows strong potential in preventing relapses of various cancers. A magnetic hydrogel with optimal adaptive functions is reported for the prevention of breast cancer postoperative recurrence. It overcomes the possible side effects of traditional magnetic hydrogels, exhibiting high inductive heating and remarkable rheological properties simultaneously. The utilization of unique properties of nanoscale materials to construct hydrogel formulation is critical for developing high‐efficient therapeutic approaches for postoperative recurrence and metastasis.