Background Cauda Equina Syndrome (CES) after Combined Spinal-Epidural Anesthesia(CSEA) is a rare disease that most of the time need surgery to relieve spinal cord compression. Case Presentation A 34-year-old male patient underwent a procedure for prolapse and hemorrhoids (PPH) under CSEA. Anesthesia and surgery were uneventful. However, the patient gradually experienced urinary retention, lower abdomen and back pain, changes in bowel habits and neurological dysfunction of the lower limbs when the catheter was removed. It was later determined that the patient had Tarlov cyst at the left S1 level in the sacral canal. Finally, the patient completely recovered 20 days after drug conservative therapy onset. Conclusion This case suggests that CES might occur even after ordinary CSEA. The risk factors are drug neurotoxicity to ropivacaine and Tarlov cyst, which helped to accumulate ropivacaine. The development of ultrasound-guided CSEA and an ultrasound atlas of the spinal canal are required.