SLE is an autoimmune disease in which a variety of autoantibodies appear in the blood and can react immunologically with tissues and cells in the body to form antigen-antibody complexes, resulting in tissue and organ damage. This immune reaction requires the participation of complement. If the disease is severe, the immune response will also be severe, and the complement will be consumed in large quantities, resulting in a decrease in complement in the blood, especially in C3 and C4. A decrease in C3 and C4 indicates that the disease is not under control, and the complement is being consumed all the time, which is an indicator of the activity or severity of the disease and indicates that further treatment is needed. However, clinically, the disease cannot be judged only by this one indicator of complement. The judgment of lupus erythematosus disease is a process that integrates clinical manifestations, laboratory tests, patients’ feelings and doctors’ judgment. Whether and how to adjust the treatment, of course, it is best to adjust the treatment appropriately according to various examination results under the guidance of professional doctors, and never adjust it by oneself, or even need hospitalization if necessary.