Colorectal cancer (CRC) is the most common gastrointestinal tract cancer worldwide and is associated with high morbidity and mortality. The development of nanosized drug delivery systems has provided a new direction in CRC treatment. Among these systems, magnetic nanoparticle (MNP)-based multifunctional platforms provide a novel strategy for magnetic resonance imaging (MRI)-related cancer theranostics. At the beginning of this original review, the carcinogenesis and treatment status of CRC are summarized. Then, diversified preparation and functionalization methods of MNPs are systematically analyzed, followed by MRI-involved theranostic strategies. The latest progress in MRI-mediated multimode diagnosis and image-guided targeted therapy in CRC management is the main focus. Finally, the major challenges in promoting MRI-induced precise theranostics of CRC in clinical practice are discussed.