Objective To discuss the preservation of petrosal vein and its clinical significance in the microsurgical operation of acoustic neuroma. Methods 147 patients with acoustic neuroma were operated, with internal decompression of the tumor firstly then dissected the tumor from surrounding structures. The petrosal vein was protected well in 143 cases and failed in 4 cases. Results No cerebellar hemorrhagic infarction was observed in 143 cases and the petrosal vein was preserved. One case occurred with extensive cerebellar edema, which had gait disturbance after 18 months followup. The other three cases occurred with vein infarction and hemorrhagic edema after petrosal vein damage. One was dead and the other two were recovered well after decompression of posterior cranial fossa. One had no significant neurological deficit after 33 months followup, while the other had difficulty in line walking after 12 months followup. Conclusion Petrosal vein should be well protected in the operation of acoustic neuroma; the decompression of posterior cranial fossa should be considered if petrosal vein failed to protect.