Brain is one of the most common metastatic organs of lung cancer. 20% to 65% of lung cancer patients will have brain metastasis during the course of the disease. When patients have some of the following symptoms related to brain metastasis, they need to suspect the occurrence of brain metastasis. The symptoms of brain metastasis include two categories: one is intracranial hypertension symptoms, including dizziness, headache, nausea, vomiting, diplopia, irritability and apathy; the other is symptoms caused by occupancy, including weakness of limbs, hemiparesis, decreased muscle strength, epilepsy, balance disorder, ataxia, blindness, language disorders such as aphasia, emotional disorders, memory loss and so on. The specific manifestations are as follows: (1) Headache: It is relatively severe in nature and often strikes in the early morning, sometimes waking up with pain during sleep, but the headache gradually relieves or disappears after getting up and moving around lightly. (2) Vomiting: Due to the increase of intracranial pressure, the vomiting center of the medulla oblongata is stimulated, resulting in vomiting, which mostly occurs after the headache, in the form of jets with high pressure, and is not obviously related to eating. (3) Visual impairment: Increased intracranial pressure can cause poor venous blood flow to the eye, leading to bruising and edema, which can damage the visual cells in the retina of the fundus, resulting in decreased visual acuity, visual field defects, red-green vision, diplopia, etc. (4) Mental abnormalities: Brain tumors located in the frontal lobe of the brain can disrupt the mental activities of the frontal lobe, causing mental abnormalities such as excitement, agitation, depression, repression, amnesia, and fiction. (5) Unilateral limb sensory abnormalities or weakness: The parietal lobe located in the middle of the cerebral hemisphere is specialized in sensation, and tumors in this area often cause unilateral limb pain, temperature, vibration, and form discrimination sensation to be reduced or lost. (6) Phantom smell: Tumor in the temporal lobe can cause phantom smell under its stimulation, i.e. smell an odor that does not exist, such as burnt rice or burnt rubber. (7) Hemiplegia or staggering gait: Cerebellar lesions are more specific, i.e. patients often develop hemiplegia or staggering drunken gait after headache, vomiting and visual disturbance. (8) Tinnitus and deafness: These are mostly detected during phone calls, i.e., one ear can hear and the other ear cannot hear. This manifestation is mostly a precursor of auditory nerve invasion. (9) Seizure: it can be generalized clonic grand mal seizure or limited seizure, frontal lobe tumor is more common, followed by temporal lobe and parietal lobe tumor. When lung cancer is diagnosed with the above symptoms, brain enhancement magnetic resonance examination should be performed to assist the diagnosis, and if necessary, lumbar puncture and cerebrospinal fluid examination should be performed to assist the diagnosis.