ObjectiveTo summarize the clinical experience of retropancreatic tunnel established by superior mesenteric vein-approach in a child with cavernous transformation of the portal vein (CTPV) during Rex bypass. MethodThe retropancreatic tunnel was created by the superior mesenteric vein-approach during Rex bypass in a child with CTPV who was admitted to our hospital in September, 2023. Clinical data were retrospectively analyzed. ResultsFor the 4-year-old male child who was diagnosed with CTPV, after the establishment of the retropancreatic tunnel by superior mesenteric vein-approach, the portal vein was quickly identified, thus simplifying the portal dissection. The operation time of Rex bypass was about 8 hours, and intraoperative blood loss was about 60 mL. After a 3-month follow-up, the child recovered well with patent bypass vessels. ConclusionThe surgical strategy proposed by our team can simplify the Rex bypass, resulting in more rapid and safe access to the vascular anastomosis site.