Micronodule in the upper lobe of the left lung refers to a dense shadow of unknown nature with diameter less than 5mm found in the upper lobe of the left lung during the imaging examination of chest and lung, which may be caused by lung cancer, tuberculosis, pneumoconiosis and other diseases. 1. Lung cancer: it is a common malignant tumor, which can be divided into adenocarcinoma, squamous carcinoma, small cell carcinoma and so on. There may be symptoms such as hemoptysis, cough and sputum, fever, etc. Imaging examination may show nodular shadows with irregular shape and irregular edges. 2. Tuberculosis: it is a kind of respiratory infectious disease caused by infection with Mycobacterium tuberculosis. There may be symptoms such as night sweating, low-grade fever, lethargy and fatigue, etc., and there may be tiny nodular shadows in imaging examination. 3. Pneumoconiosis: It is a lung fibrosis disease caused by inhaling dust for a long time or too much. There are symptoms such as dyspnea, chest pain, etc. Imaging examination may show round or irregular shaped nodular shadow. It is recommended to carry out further examination under the guidance of doctor, and receive timely and symptomatic treatment after identifying the cause.