Objective To investigate the pathogenesis, clinical diagnosis and treatment of immunemediated necrotic myopathy（IMNM）. Methods A female patient diagnosed as IMNM by skeletal muscle biopsy was treated with corticosteroids. The hospitalization and outpatient follow-up information were analyzed. Results The patient was followed up for 22 months，and myopathy was quickly relieved after corticosteroids treatment and nephropathy was clinically relieved after prednisone combined with immunosuppressive therapy. The nephrotic syndrome was stable and the myopathy was not recurring after stopping the drug for a long time. Conclusion IMNM is caused by autoimmune abnormalities. Skeletal muscle biopsy is the main method for diagnosis, and IMNM responds well to glucocorticoid therapy. And during the treatment, attention also should be paid to the treatment of comorbidities that may cause immune disorders further.