Chest X-ray is relatively more harmful to human body compared with CT. Chest X-ray is the oldest traditional examination item, and it is not comparable to CT in terms of performance, function and safety of the equipment. When doing chest X-ray, both the doctor and the patient are exposed to great radiation from X-rays, so chest X-ray is now not used as a routine examination in larger hospitals. CT as a more advanced imaging equipment, radiation measurement is within the safe range, the harm to human body is very small.