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To investigate the stress evolution, deformation behavior, and failure characteristics of composite-reinforced prestressed concrete hollow square piles (PHSC piles) under bending, a four-point bending test was conducted on a full-scale PHSC500 (340) hollow square pile specimen with a length of 7000 mm, a square section of 500 mm × 500 mm, and a hollow core diameter of 340 mm. The test was used to obtain load–deflection curves, crack propagation patterns, deformation responses, sectional strain distributions, and failure modes. In addition, an ABAQUS finite element model was established to compare the bearing capacity, stiffness degradation, and ductility of different pile types with varying prestressed and non-prestressed reinforcement ratios. The results show that vertical cracks changed their propagation direction at the edge of the tensile zone in the flexural–shear region of the PHSC piles and developed into a critical diagonal crack with a width of 1.7 mm. The specimen ultimately exhibited a shear–compression failure mode. During the failure stage, the midspan deflection increased rapidly as the load rose from 710 to 740 kN, with the deflection increasing from 24.88 to 32.00 mm. The load–midspan deflection curve obtained from the finite element analysis was generally consistent with the experimental results. Moreover, the predicted damage concentration zones corresponded well to the experimentally observed crack locations, indicating that the model can be used to analyze relative variations under different parameter conditions. The combination of prestressed and non-prestressed reinforcement improved the flexural capacity and ductility of the PHSC piles. However, ductility did not increase monotonically with the prestressed reinforcement ratio. These findings provide a reference for evaluating the flexural performance of PHSC hollow square piles and optimizing their reinforcement parameters. Full article