The invention discloses a T1-T2 double quenching-activation MRI contrast agent and a preparation method thereof, the MRI contrast agent has a core-shell structure, the core-shell structure sequentially comprises a T2 layer composed of a T2 contrast agent, an MOF structure layer composed of metal organic framework particles and a T1 layer composed of a T1 contrast agent from inside to outside, and one metal organic framework particle coats one T2 contrast agent; the T2 contrast agent is superparamagnetic iron oxide nanoparticles, the T1 contrast agent is a gadolinium-containing ionic compound or a manganese-containing ionic compound, and the dosage ratio of Fe in the T2 contrast agent to Gd or Mn in the T1 contrast agent is 1: (10-40). The MRI contrast agent provided by the invention can realize significant difference imaging signals between normal tissues and acidic lesion tissues, so that the purpose of imaging detection is achieved, and the MRI contrast agent has higher sensitivity, higher response speed and higher release efficiency.