There are obvious differences between pneumonia and lung cancer on CT. Pneumonia mostly appears as a lamellar shadow with low density and irregular shape, while lung cancer appears as a soft tissue mass with higher density and irregular shape with short burrs around. For example, those with fever, cough and chest pain are mostly lung infections, and after anti-infection treatment, lung inflammation shadow will be dissipated and absorbed, while lung cancer is not effective through anti-infection treatment, and the main symptoms are cough and blood in sputum, and cancer cells can be found by fibrinoscopy or pathological puncture biopsy, which can confirm the diagnosis of lung cancer. In conclusion, there is a certain difference between CT film pneumonia and lung cancer, sometimes lung cancer can also show the imaging changes of obstructive pneumonia, at this time, the basis of diagnosis is pathological puncture biopsy or fiberoptic bronchoscopy.