The decrease of single complement C3 can be seen in systemic lupus erythematosus, glomerulonephritis, cirrhosis, etc. It is recommended to consult a doctor in time, and choose the appropriate medication under the doctor’s guidance. 1. Systemic lupus erythematosus: symptomatic treatment, such as non-steroidal anti-inflammatory drugs such as diclofenac sodium, etc., can be prescribed to relieve fever and pain, etc., and glucocorticosteroid treatment is feasible for patients with severe diseases, or immunosuppression such as cyclophosphamide is preferred. 2. Glomerulonephritis: for acute cases, diuretics such as spironolactone are mainly chosen to reduce blood pressure; for progressive nephritis, plasma exchange or methylprednisolone shock therapy can be chosen. 3. Cirrhosis: reduce protein intake, use adenosylmethionine, polyenylphosphatidylcholine to protect hepatocytes, and actively stop bleeding points, such as taking medications such as octreotide and growth inhibitors. It is recommended that patients who have a single complement C3 decrease should consult the doctor in time, complete the relevant examination under the guidance of the doctor, clarify the cause of the disease and early treatment.