The invention discloses a magnetic nanoparticle compound for a T1 and T2 bimodal magnetic resonance contrast medium and a preparation method thereof. The magnetic nanoparticle compound is of a three-layered core-shell structure. The cores are Fe3O4 nanoparticles, the middle layer is a silicon dioxide layer of manganese-porphyrin hydrochloride, and the outermost layer is an acrylic acid polymer layer of cyclopeptide radial-cRGD of a targeted integrin receptor. The preparation method comprises the following steps: 1, preparing OA@Fe3O4@nSiaO2@mSiO2; 2, preparing OA@Fe3O4@nSiO2@mSiO2@PAA-cRGD; 3, preparing manganese-porphyrin hydrochloride; and 4, preparing Mn-IOSP. The magnetic nanoparticle compound is used for preparing a new generation T1 and T2 bimodal magnetic resonance contrast medium which is high in relaxation rate, low in toxicity and long in circulating time. The magnetic nanoparticle compound can improve the imaging performance and accuracy, and has good biocompatibility.