A Study of IBI311 in Subjects With Inactive or Active Thyroid Eye Disease

Key Inclusion Criteria: 1. Written informed consent. 2. Male or female subject between the ages of 18 and 80 years at screening. 3. Weight between 50 kg and 100 kg. 4. Moderate-to-severe active TED: * CAS ≥ 3 in the study eye at screening and baseline; * Usually associated with at least two of the following: lid retraction ≥ 2 mm, moderate or severe soft tissue involvement, exophthalmos ≥ 3 mm above normal, and/or inconstant or constant diplopia; * ≤ 12 months since the onset of active TED symptoms according to subjects' chief complaint or medical record at screening; Inactive TED: * According to subjects' chief complaint or medical record at screening, initial diagnosis of TED \> 12 months but \< 10 years prior to screening. * CAS ≤ 2 in both eyes at screening and baseline and CAS ≤ 2 in both eyes for at least 6 months prior to screening or all of the following at least 6 months prior to screening: a. no progression in proptosis; b. no progression in diplopia; c. no new inflammatory TED symptoms. * Exophthalmos ≥ 3 mm above normal. 5. Exophthalmos ≥ 20 mm in the study eye at baseline. 6. Female subjects should be fertile women who are sterile or have a negative blood pregnancy test during the screening period and who agree to take contraceptive measures within 120 days from the screening period to the last medication; Male subjects should agree to use contraception from the screening period to 120 days after the last dose. Key Exclusion Criteria: Subjects will be ineligible for study participation if they meet any of the following criteria: 1. Baseline CAS decreased by ≥ 2 points, or baseline proptosis decreased by ≥ 2 mm as compared with screening. 2. Visual function impairment due to optic neuropathy, defined as ≥ 2 lines of vision loss, new visual field defect, or color vision impairment secondary to optic nerve involvement within the past 180 days; 3. Corneal ulcers with no relief after treatment as determined by the investigator; 4. TED patients who need immediate corticosteroid therapy, orbital radiotherapy, or orbital decompression; 5. At any time prior to baseline or during the study period planned to receive orbital radiation therapy or TED surgery, including orbital decompression, strabismus surgery, and eyelid retraction correction; 6. Poorly controlled thyroid function, which was defined as free triiodothyronine (FT3) or free tetraiodothyronine (FT4) deviated more than 50% from the normal reference range of the local research center laboratory at screening. 7. Either ear had a history of tinnitus or other hearing impairment; or abnormal pure tone audiometry (defined as mean bone conduction threshold \[0.5, 1, 2, 4 kHz\] ≥25 dB or any bone conduction threshold ≥ 40 dB); 8. Poorly controlled diabetes at screening, defined as HbA1C ≥ 9.0% at screening, or any new medication for diabetes within 60 days prior to screening, or any dose adjustment for diabetes drugs \> 10%); 9. Systemic use of glucocorticoids ≤ 30 days prior to screening; 10. Periorbital use of glucocorticoids ≤ 90 days prior to screening; 11. Systemic use of immunosuppressants ≤ 90 days prior to screening; 12. Use glucocorticoid eye drops or immunosuppressive eye drops ≤ 30 days prior to screening 12\. Use IBI311 or TEPEZZA at any time prior to screening; 13 Use CD20 antibody ≤ 1 year prior to screening, or IL-6R antibody ≤ 180 days prior to screening; 14. Subjects had participated in other interventional clinical trials ≤ 90 days prior to screening, or attempting to participate in other clinical trials during the study period.