[Abstract] Objective: By microanatomy?research on structures in various sections of suboccipital retrosigmoid?Keyhole via approach of petrosal fissure and cerebello-pontine fissure， so as to provide anatomy data for clinical application.Methods: 15 wet head specimens of 30 normal adults were dissected: the approach operation was simulated， the cadaveric heads were fixed onto head shelf in lateral?position， retromastoid?transverse (vertical) incision was adopted， then a bone window of 2.5cm-3cm was opened， to incise endocranium and measure change of operation field exposure scope， exposed situations of trigeminal?nerves， facial?and auditory nerves and glossopharyngeal nerves at place where such nerves enter brainstem before and after separation of petrosal fissure and cerebello-pontine fissure； petrosal fissure and ramus?inferior and ramus?superior of cerebello-pontine fissure were dissected under microscope； research objects concerninig petrosal fissure， ramus?inferior and ramus?superior of cerebello-pontine fissure， petrosal?vein， cerebellar?arteries， trigeminal?nerves， facial and auditory?nerves and glossopharyngeal nerves at place where such objects enter brainstem were measured， and photos were taken.Results: The exposed anatomical structures by this Surgical approach: upwards to tentorial edge， downwards to foramen magnum jugular tuberculum， inwards to lateral side of pons?and midbrain. Cerebellopontine?angle?area including petrosal?vein， upper， middle and lower neurovascular?territories of cerebellum were exposed. Distance between before and after separation of petrosal fissure and cerebello-pontine fissure is of statistical difference.Conclusion: This Surgical approach is the supplement and enlargement of typical retrosigmoid?approach，with small incision and less brain injury， it can fully utilize the natural space of epencephalon， so as to increase operation space on the premise of not pulling or less pulling epencephalon； this Surgical approach is operable in anatomy in microvascular decompression treatment of cranial nerve disease，this Surgical approach can make the structures in relevant area of posterior cranial fossa more exposed， to provide anatomy space for excision of space-occupying lesions in cerebellopontine angle area.