Advanced malignant tumor metastasis to the brain is a common clinical phenomenon, and tumor metastasis to the brain is likely to be accompanied by metastasis to other parts and organs throughout the body. The size, number and location of the lesions metastasized to the brain and the whole body are crucial to the formulation of a reasonable treatment plan and need to be evaluated comprehensively and carefully. After a malignant tumor metastasizes to the brain, it is necessary to clarify whether the lesion in the brain is a metastatic lesion or a primary lesion, and another important element is the number and size of metastatic lesions in the brain and other parts of the body. For malignant tumors that metastasize to the brain, most of the symptoms are caused by the compression of nerve structures or increased intracranial pressure in the brain. The number, size and location of brain lesions can be accurately assessed by MRI, which is also an important basis for brain treatment planning. For single lesions or smaller than 3 lesions in close proximity to the brain that are estimated to be insensitive to radiotherapy, they can be surgically removed at once to achieve better results. For smaller or more numerous lesions, radiotherapy is usually needed to treat them or to delay radiotherapy with systemic targeted drugs. The development of the best treatment plan for metastatic brain lesions requires assessment of the tumor throughout the body in addition to the examination of the brain lesions. Currently, PETCT is a more comprehensive test to evaluate the systemic metastasis of malignant tumors, but for small metastatic lesions, this test still has the possibility of missing the diagnosis. Of course, for certain key areas, targeted examinations can be used, such as whole body bone scan to check bone metastasis. There are also specific tumor markers for some malignant tumors, and the level of tumor markers can be used to understand the situation of primary or metastatic lesions. After a malignant tumor metastasizes to the brain, a comprehensive assessment of the brain and metastatic lesions outside the brain is needed to develop an appropriate treatment plan. Surgical resection, radiotherapy and targeted or immunotherapy can be used after malignant tumors metastasize to the brain. Only after comprehensive assessment of brain and systemic status, a reasonable plan can be formulated to avoid over-treatment or insufficient treatment intensity to achieve the best treatment effect.