Polymyositis is an autoimmune disease with muscle weakness and myalgia as the main manifestations. It mainly affects the limb band muscles, cervical muscles, and throat muscles. The main symptoms are muscle pressure, laryngeal muscle weakness, and myalgia. Polymyositis may be related to infection, abnormal body immunity, vascular lesions, genetic factors, etc. 1, the body immune abnormalities muscle biopsy specimens found to have immunoglobulin, complement deposition and inflammatory cell infiltration; elevated immunoglobulin in the blood, anti-nuclear antibodies, rheumatoid factor, anti-J0-1 and other autoantibodies positive, etc. indicate that the development of the disease is related to immune abnormalities. 2, infection bacteria, viruses, fungi, protozoa and other infections may be related to the development of the disease, especially viral infections can cause disruption of the immune apoptosis response in the body, producing skin, muscle and visceral lesions. 3, child-type dermatomyositis vascular lesions are more prominent. 4, genetic factors Although studies have been reported, but so far not enough to indicate polymyositis or dermatomyositis has a genetic predisposition. It has been found that the HLA-B27 gene is present at a higher rate in adults with polymyositis and in children with dermatomyositis. In addition, malignant tumors, immunizations, drugs, alcoholism, trauma, surgery and some endocrine disorders can also cause non-specific inflammation with skin and muscle as the main lesions, inducing the development of the disease.