Objective To study microanatomy of related structure of transcerebellomedullary fissure approach (trans-CMF approach), and refine the trans-CMF approach to obtain an appropriate operative view without splitting the inferior vermis, We have adopted the trans-CMF approach to remove the lesions located in the foramen of magnum, cerebellomedullary fissure (CMF) and the fourth ventricle in clinical application. Methods we adopted the trans-CMF approach for use in 20 cases of the lesions located in the foramen of magnum、CMF、fourth ventricle、dorsolateral to the pons and medulla, based on operation method and prognosis ,we describe and analyse degree of resection and exposure of extent relative region, three illustrative cases are presented. Results We adopt extensive opening method(11cases), lateral wall opening method(7cases), lateral recess opening method(2cases)by trans-CMF approach. the exposure of lesions region show sufficiency(16cases), localization(2cases) difficulty(2cases), it also shows remove totally( 10cases), remove mostly(6cases), remove partly(4cases). Glasgow outcome scale of the patient after leaving hospital is 5 points(12cases), 4 points(8cases).postoperative pathology have ependymoma(6cases), astrocytoma (3cases), medulloblastoma(3cases), cavernoma(3cases), epidermoid cyst (2cases), Ch Pl papilloma(1case), hemangioblastoma(1case), arterio-venous malformation(1case). Conclusion Trans-CMF approach provides a sufficient operative view from the fourth ventricle to dorsolateral part of the pons and medulla through normal anatomic spaces and reduce the lesions of nervous tissure and postoperative complications.