Current treatment options for posttraumatic syringomyelia (PTS) lack clear standardization and often result in common complications. This study aims to introduce a novel minimally invasive technique for a modified subarachnoid-subarachnoid (S-S) bypass procedure for PTS.The study included 20 consecutive patients with symptomatic PTS who underwent the modified S-S bypass. The surgical technique of modified S-S bypass involved two-laminae fenestration based on preoperative MRI and myelography results showing normal subarachnoid space above and below the injury site. A passer was used to create a subcutaneous tunnel, and two medical-grade silicone tubes were inserted into the normal subarachnoid space at the cranial and caudal ends. Bypass tubes were placed in the subcutaneous tunnel, and dural closure was achieved using 6-0 nonabsorbable sutures. The mean follow-up period was 14.9 (range 12-18) months, with neurological function assessed using a standard grading system and MRI used to evaluate the change in syrinx size.Seventeen patients demonstrated clinical improvement, while 3 remained stable. The mean preoperative syrinx length on MRI was 16.9 spinal levels, with a mean Syringomyelia Tension Index (STI) of 58.1%. The postoperative mean STI was 28.4%, significantly lower than preoperative values (p < 0.05).Modified S-S bypass, which can be performed without myelotomy and without the bypass tubes interfering with the adhesion, was not only a safe and effective surgical technique, but may also be a physiologically better way of treating PTS.