The purpose of this study was to explore the innervations of different sacral nerve posterior roots to bladder, and to provide evidence for further study of skin-CNS-bladder reflex pathway in the spinal cord injury patient. Spinal cord injury was produced in 10 rats. The bilateral spinal posterior roots of S1-S4 were electrically stimulated, and the bladder plexus action, bladder smooth muscle complex action potential, and intravesical pressure were examined and measured. The results showed that all the sacral nerve posterior roots were involved in innervations of bladder in rats. Among them, the S2 sacral nerve is the dominant nerve in innervations of bladder, followed by S1, S3, and S4 sacral nerve posterior roots. This study has provided valuable information for selection of sacral nerve posterior root for further study of the artificial bladder reflex arc for improving the micturition function in spinal cord injury patients.