Abstract: Brain metastatic tumor is a kind of intracranial tumor. It refers to the tumor cells which originated in other parts of the body through some way to transfer to the brain and form new foci in the brain. Early diagnosis and differentiation of brain metastasis is essential for timely treatment, prolongation of life and improvement of patients undefined quality of life. MRI has the advantages of non-radiation, multi-directional, multi-sequence and high soft tissue resolution. Especially, the development of functional imaging and the application of new techniques make it play an important role in the diagnosis, differential diagnosis, monitoring and evaluation of the prognosis of brain metastases. This review focuses on the application of MR functional imaging and new techniques in the detection of small metastases, differential diagnosis of brain metastases and curative effect monitoring.