Abstract： Objective The spatial location of nerve fibers of various trigeminal branches in the posterior root were studied using electrophysiological monitoring.Methods This clinic study included 20 cases of trigeminal neuralgia patients receiving microvascular decompression surgery.During operation,the rostral,caudal,dorsal and ventral parts of the root entry zone of trigeminal nerve were stimulated respectively.The compound nerve action potentials were recorded in supraorbital,infraorbital and mental foramina simultaneously.Then the waves recorded from each peripheral branch were analyzed.Results Different parts stimulated,the occurrence of the compound nerve action potential wave was different.According to electrophysiological monitoring,the V1 fibers were mainly located in the rostral part,the V2 fibers in the rostral dorsal and ventral parts,and the V3 fibers in the caudal ventral and dorsal parts.The electrophysiological data were in accordance with the symptoms and the vascular compression location.Conclusion Recording compound nerve action potentials through antidromic electrical stimulation can help to locate the various branches of the trigeminal nerve in the posterior root,to identify causal vessel,and to provide reference for microvascular decompression surgery.