Inclusion Criteria:  Clinical diagnosis of primary grade 3-4(according to MAGIC criteria) steroid-resistant acute graft-versus-host disease(progression after 3 days or lack of improvement after 5 days of systemic 1.5-2 mg/kg steroids). Age 18-65. ECOG score≤3. Must be able to understand and willing to participate in the study and sign the informed consent.  Exclusion Criteria:  Refractory/secondary graft-versus-host disease. Severe complications such as myocardial infarction, chronic cardiac insufficiency, hepatic failure, renal insufficiency, etc. Clinically uncontrolled active infections. Other Malignant tumors with progression. Ecg: QT interval > 450 ms. Allergic to arsenic agent. Pregnant or lactating women. Expected survival <60 days. Undergoing other drug clinical trials.