Abstract: To systematically investigate the influence of behind-lining voids on the mechanical performance of fully prefabricated shield tunnels, a refined three-dimensional finite element model of the soil-segment-internal structure system was established based on the Hai-Tai Yangtze River Tunnel. The results show that the presence of voids causes stress concentration at the corresponding segment locations, resulting in a bullet-head-shaped deformation pattern of the segments and a butterfly-shaped distribution of bending moments. The influence of void location on segment deformation decreases in the order of the spandrel, crown and invert. In the absence of internal structures, the maximum deformation induced by a spandrel void reaches 21.649 mm. The internal structure increases the axial force of segments near the void and effectively restrains segment deformation. Under the spandrel-void condition, the segment deformation is reduced by 54.1%. Voids also alter the bending-moment distribution of the segments, leading to a sign reversal of the bending moment at the crown and an increase in bending moment at the spandrel. In addition, the internal structure reduces the bending moment of segments near the spandrel void and improves the sectional bearing capacity. In terms of structural safety, the safety factors of segment sections with internal structures are generally higher than those without internal structures. Under the spandrel-void condition, the safety factors are 1.537 and 1.252, respectively, and all calculated cases remain in a safe state.