Abstract: A case of severe bone marrow inhibition in the treatment of differentiated thyroid cancer (DTC) by radionuclide ¹³¹I was reported. The characteristics of the case were analyzed based on clinical diagnosis, changes in bone marrow hematopoietic system, and whether the patient's treatment process was standardized. The therapeutic effect of radionuclide ¹³¹I in the diagnosis and treatment of DTC bone metastasis and the effect of bone marrow hematopoiesis were reviewed. Radionuclide ¹³¹I had considerable clinical effect on the diagnosis and treatment of DTC bone metastasis. However, with the increase of cumulative dose and the difference of sensitivity of patients to ¹³¹I treatment, white blood cells or platelets in the bone marrow hematopoietic system may decrease. For the treatment of ¹³¹I patients with extensive bone metastasis, the occurrence of bone marrow inhibition should be on highly alert and the cumulative treatment dose should be considered. The interval between retreatment should be maximized. When bone marrow inhibition occurs in patients with extensive bone metastasis, ¹³¹I treatment should be used selectively.