Hyperperfusion injury is a major contributor to small-for-size syndrome (SFSS) following liver transplantation, particularly in left-liver transplantation (LLT). Given donor preservation constraints, “left-at-right” liver transplantation (LAR-LT) has emerged as a potential strategy to mitigate this complication. This study employed computational fluid dynamics (CFD) to investigate the mechanical mechanisms underlying SFSS in five patients who underwent LLT at Beijing Friendship Hospital. Patient-specific portal vein blood flow models for conventional LLT and LAR-LT were developed using computed tomography (CT) imaging and finite volume simulations. Perfusion loss in recipients was assessed through pressure analysis, while mechanical differences between the two transplantation techniques were evaluated based on portal vein streamlines. The results demonstrated that rotating the left liver to the right-liver position significantly reduced portal vein pressure, with statistically significant differences observed as portal vein flow rate increased. Mechanical analysis further revealed that LAR-LT promoted smoother portal vein streamlines and reduced vortex formation, thereby alleviating hyperperfusion-related injury. These findings suggest that LAR-LT effectively prevents hyperperfusion injury and reduces the incidence of SFSS, while CFD-based simulations provide a valuable tool for modeling complex clinical scenarios and optimizing liver transplantation strategies.