The invention discloses iodinated pituitary resistance to thyroid hormone (PRTH), and a preparation method and application thereof, relates to a tumor/cancer diagnosis and treatment reagent, and belongs to the field of medicine and pharmacology. By combining nanotechnology and molecular nuclear medicine, the PRTH is iodinated; and the enhanced permeability and retention (EPR) effect of the PRTH is used for early diagnosis and early treatment of tumor/cancer. The iodinated PRTH has the advantages of simple preparation process, stable marker, safety, no toxicity and good targeting of the tumor/cancer.