Clinical diagnosis is often supported by the accurate registration and fusion of CT and MRI images. In this paper , a distance transformation (DT) is applied to the verge of the natural brain tissue in the CT image, firsuy.Then the registration is accomplished by using the verges of the natural brain tissue in MRI - T1 and MRI - T2 images as polygons. As a result , the fusion of the complementary information in the CT and MRI is achieved. The algorithm used in this paper is applicable to the registration of CT and MRI images. At the same time , it can be a reference for the matching of other medical images such as SPECT ,PET and DSA.