Intracranial metastases are more common in middle-aged and elderly people, most often between the ages of 40 and 60. The most common primary tumor is lung cancer. In addition, breast cancer, choriocapillary epithelial cancer, thyroid cancer, kidney cancer, melanoma, etc. are also more common. The reason why brain metastasis from lung cancer is so common, besides the high incidence of the tumor itself, a very important reason is that tumor cells can enter the body circulation directly from the pulmonary veins, while other tumors must first pass through the filter of the pulmonary circulation. Because of its high density resolution, convenient examination and high diagnostic accuracy, CT examination is now widely used as a routine examination in clinical practice. If we can understand the relationship between clinical manifestations and CT examination of lung cancer brain metastasis patients and give full play to the advantages of CT examination, it can not only improve the diagnosis, but also be of great significance to the patient’s selection of treatment plan and prognosis. We often encounter the following situations in daily CT examinations: 1. Patients who are clinically suspected to have “cerebral infarction” or “cerebral hemorrhage”, but the CT examination results are single or multiple occupying lesions in the brain, and then lung cancer is found in the examination of lungs. 2. 2. Some patients who were clinically diagnosed as benign lung lesions such as “pneumonia, tuberculosis or lung abscess” suddenly developed neurological symptoms during treatment or when their clinical symptoms had improved, and were found to have single or multiple occupying lesions in the brain by cranial CT examination. In turn, further examination of lung lesions such as bronchoscopy, chest CT, biopsy, etc. will confirm the diagnosis of brain metastasis of lung cancer. 3. For patients who are diagnosed with lung cancer and have undergone surgical resection, neurological symptoms appear after discharge from the hospital and are found to be brain metastases by CT examination. In some patients with lung cancer, brain metastases were found in cranial CT examination one week after surgery. We presume that the patients already had brain metastases before surgery, but just did not show clinical symptoms. One of the reasons why clinicians did not perform cranial CT examination on lung cancer patients before surgery is that they did not know enough about “prior” lung cancer brain metastases and did not pay attention to asymptomatic brain metastases, which is very important for determining the treatment plan. Imagine if a lung cancer patient has multiple metastases in the brain before the surgery, and then the patient is operated to remove the lung cancer, it will cause financial loss to the patient on one hand, and the treatment effect is not ideal on the other hand. In order to give full play to the role of CT examination in the diagnosis of lung cancer and its prognosis, especially the value of CT examination in the application of “prior” lung cancer brain metastases, and to draw the great attention of clinicians in primary hospitals, we propose the following suggestions with our own working experience over the years: 1. For patients with “cerebral infarction” or “cerebral hemorrhage”, if they are found to have multiple occupancies in CT examination, we should suggest them to have further pulmonary X-ray or chest CT to exclude the possibility of pulmonary occupancies, which not only shortens the examination time but also provides the basis for further clinical treatment. This will shorten the examination time and provide the basis for further treatment. 2. For some “benign” lesions in the lung, if patients have central nervous system symptoms during treatment, a cranial CT examination should be performed in a timely manner. If multiple occupations are found in the brain, further examination of the original lung lesions should be conducted, such as bronchoscopy and sputum examination for cancer cells, in order to exclude the possibility of occupying lung lesions and avoid misdiagnosis. 3 . For patients who have been clinically diagnosed with lung cancer, regardless of the presence or absence of neurological symptoms, they must routinely undergo cranial CT examination before surgery to avoid unnecessary traumatic treatment. For postoperative patients with lung cancer, regular cranial CT examination should be performed to observe whether there is metastasis in the brain at any time for symptomatic treatment. In conclusion, patients have a variety of clinical manifestations, especially a few patients whose first symptoms are neurological manifestations, and the primary lesion may not always be in the brain, so CT examination not only plays an important role in differential diagnosis, but also can guide further clinical examination. For “inflammatory” lesions in the lung, if they are not absorbed by long-term treatment, further examination should be performed to avoid misdiagnosis, among which cranial CT examination can exclude “prior” brain metastases. Clinicians should routinely perform cranial CT examination before surgery for patients diagnosed with lung cancer, and regular CT review after surgery is of great value to patients and prognosis.