Since the current 5-year survival rate of lung cancer patients is not high and most of them are already in advanced stage when diagnosed, only by improving the early diagnosis rate can the prognosis be significantly improved. 1. Early symptoms and signs of lung cancer: For smokers with the following clinical features, especially those over 40 years of age, they should immediately take corresponding examinations for early diagnosis and differential diagnosis: (1) irritating cough lasting for more than 2 weeks, which is ineffective in treatment; (2) pre-existing chronic respiratory diseases with recent changes in the nature of cough; (3) unilateral restricted croup, which does not change due to cough; (4) repeatedly the same part pneumonia, especially segmental pneumonia; (5) unexplained lung abscess without history of foreign body inhalation and toxic symptoms and poor antibiotic treatment; (6) unexplained joint pain and pestle fingers/toes; (7) imaging findings of limited emphysema with no rise of lobes or segments of the lung and suspicious stenosis of the communicating bronchi; (8) isolated round, round-like lesions and unilateral hilar shadow enlargement and thickening; (9) Original stable pulmonary tuberculosis lesions, new lesions appear in other parts of the body, and the lesions instead increase in size or form cavities after anti-tuberculosis treatment, with negative sputum tuberculosis bacteria; (10) unexplained migratory, embolic lower limb phlebitis. 2.Imaging: When the central type tumor grows into the lumen, it can cause signs of bronchial obstruction, and when the obstruction is incomplete, it presents segmental and lobar emphysema. If the obstruction is not complete, it shows segmental and lobar pulmonary atelectasis. When pulmonary atelectasis is accompanied by hilar lymph node enlargement, the lower edge may show an inverted S-shaped image. Peripheral type of lung cancer in early stage mostly shows limited small patchy shadow with indistinct margin and light density, which is easily misdiagnosed as inflammation or tuberculosis. After the tumor enlarges to 2-3 cm, it appears as a round or round-like mass with increased density and clear margins. ke appears lobulated with umbilical concave or fine burr-like shadow. High resolution CT can clearly show tumor lobulation, marginal burr, pleural indentation sign, and even calcium distribution type, bronchial inflation sign and vacuolation sign. After tumor necrosis and bronchial communication, it shows thick-walled, eccentric, cancerous cavities with uneven inner edges. Conventional chest radiographs have limited resolution and dead space, making it difficult to detect lesions smaller than 6 mm. Therefore, for those who cannot exclude lung cancer, CT examination is needed in time. 3.Cytological examination: sputum cell examination is very helpful for lung cancer. If sputum specimens are collected properly, more than 3 series of sputum specimens can increase the diagnosis rate of central type lung cancer to 80% and peripheral type lung cancer to 50%. 4.Fiber bronchoscopy: It has been widely used for the diagnosis of lung cancer. For endobronchial lesions visible by fiberoptic bronchoscopy, the diagnostic rate of brush examination can reach 92%, and the diagnostic rate of biopsy can reach 93%. 5.Needle cytology examination: Needle aspiration cytology examination can be performed percutaneously or via fibrinoscopy. Can also be guided by ultrasound, X-ray or CT, currently commonly used mainly for superficial lymph nodes and ultrasound-guided needle aspiration cytology examination. 6 Other biopsies: surgical removal of superficial lymph nodes such as supraclavicular and cervical lymph nodes for pathological examination can determine whether there is tumor metastasis and its cell type. Biopsy can also be performed through mediastinoscopy, pleural biopsy and thoracoscopy. 7.Chest dissection: For cases with high suspicion of lung cancer, if the diagnosis is not confirmed by all the above methods and can tolerate surgery, chest dissection should be performed in time to avoid losing the opportunity of surgery. 8.Nuclear medicine examination: Positron emission tomography (PET) has a sensitivity of up to 95% for lung cancer, and is also sensitive to detect metastatic lesions, with a specificity of up to 90%, and can be used as a reference basis for lung cancer staging, evaluation of treatment efficacy, and recurrence and metastasis. 9.Tumor markers: The serum and surgical tissues of some lung cancer patients contain one or more biologically active substances, which can be used for the diagnosis of lung cancer, but the individual specificity is not strong, and the combined test can help the diagnosis. Commonly used are carcinoembryonic antigen (CEA), neurospecific enolase (NSE), and cytokeratin 19 fragment (CYFRA21-1). Therefore, for those who are suspected of lung cancer, they should promptly visit the hospital to improve the examination and make a clear diagnosis at an early stage so as not to lose the time for treatment.