The invention belongs to the field of bio-medicine, and discloses a magnetic resonance imaging nano-carrier, a nano drug carrier system and a preparation method thereof. According to the invention, two targeting molecules, namely folic acid and cell-penetrating peptide, are adopted, so that a targeting effect on tumors is improved, and meanwhile, anti-tumor activity in vitro and in vivo is enhanced. PLGA, which is low in toxicity and good in biocompatibility, is taken as the anti-tumor drug carrier, and the terminal of the PLGA is modified with CS, so that the functional nano-system is prepared. Meanwhile, nuclear magnetic imaging drugs and anti-tumor drugs are effectively loaded, so that the anti-tumor drugs can reach a tumor focus part in a specific mode, and tumor region nuclear magnetic localization of ferroferric oxide nanoparticles can be implemented; and meanwhile, a therapeutic effect with high selectivity and low toxicity can be achieved. With the application of the invention,shortcomings of conventional cytotoxic drugs which are poor in selectivity, relatively strong in toxic and side effects, capable of causing drug tolerance easily and the like can be overcome; and a utilization degree of the anti-tumor drugs can be improved and toxic and side effects can be reduced. The preparation method of the drug carrier system is simple and easy to implement; and the preparedproduct (the drug carrier system) is good in repeatability and stability.