【】: Object: To summarizes the acoustic characteristics of the normal and the abnormal fetal cerebellum and cerebellum in sagittal section, To find the relationship between microbrain structure and fetal abnormalities .SMethod: In October 2014 to January 2015 we had accumulated 43 fetus In total these fetus posterior cranial fossa were fand abnormal in cross section , Using three-dimensional ultrasound to capture the stereoscopic data of a fetus"s cranial brain, Then we observed The morphological and textured features of the cerebellum and cerebellum continuously. Outcome: In these 43 cases, There were 38 fetus their posterior cranial pool were wider than 10 mm ,4 fetus their inferior worm of cerebellum were suspicioused absence,1 fetal the echo of the cerebellum was abnormal. Using the Three-dimensional ultrasound All of these cases were received the Satisfied sagittal image. In the first group There were 37 cases their cerebellum and cerebellum were normal,1caes was blacks cyst; In the second group 3 cases were diagnosed with Dandy-Walk malformation, 1caes was blacks cyst ,the last cases was diagnosed hindbrain fusion. Conclusion：IN sagittal section the normal cerebellum like a circular fan the texture’s rendezvous reach the vertices of the fourth ventricle. When this feature changed that suggestd the fetal was a freak,This feature was a mark to Prompt clinical