Abstract: MRI was used in radiotherapy of brain tumor more and more comprehensively, especially in the prognosis, radiotherapy planning and differentiation between recurrence and necrosis of brain tumor. Due to the excellent ability in the differentiation of soft tissue, MRI extensively fusing with CT was used in drawing the outline of the tumor.Maybe in the future, it is possible to use MRI absolutely in radiotherapy planning of brain tumor.With the development of the functional MRI, MRI will be a necessary method used widely in the differetion between brain tumor reccurence and radiation injury.