Pleural thickening, also known as pleural fibrosis, is an increase in the thickness of the pleura that occurs when fibrin deposits and granulation tissue proliferate as a result of a left-sided pleural lesion. Left pleural thickening usually requires no treatment, but in severe cases, surgical treatment is needed, and the primary disease should be actively treated. Left pleural thickening is associated with tuberculous pleurisy, pyothorax and other diseases, which may manifest as decreased activity endurance, obvious dyspnea, thoracic deformity and other symptoms. For patients with mild symptoms of left-sided pleural thickening, no special treatment is usually needed, and the symptoms can be relieved by rest. For patients with obvious symptoms of left-sided pleural thickening, surgery such as pleurodesis can be performed to remove the diseased tissue. If there is a primary disease, such as tuberculous pleurisy, pyothorax, etc., the primary disease needs to be actively treated. Patients with tuberculous pleurisy can use anti-tuberculosis drugs such as rifampicin, isoniazid, etc., and for patients with a lot of pleural effusion, they can be drained by thoracentesis. Acute pyothorax needs to control the primary infection and adequate drainage of pus, chronic pyothorax can be treated surgically. The left pleural thickening should go to the hospital in time, and ask the doctor to make a clear diagnosis and treatment.