Abstract: Pretensioned T-beams with folded lines exhibit high bearing capacity and long span, demonstrating broad application prospects in bridge engineering. For prestressed beams, the presence or absence of cracking is a key indicator to determine whether they remain in a normal working state. As the prestress is mainly transferred through the bonding force between steel strands and concrete, cracking can lead to direct exposure of the internal prestressed reinforcement to corrosive medium. This weakens the bonding performance and significantly compromises the structure’s durability and safety. Based on practical engineering, this study presents the design of a novel 30 m pretensioned polygonal prestressed T-beam. Through full-scale experiments and finite element model numerical analysis, the crack resistance of the inclined section at the beam end under a shear span ratio of λ = 2.5 was studied. The experiment adopted a graded loading method. Test results indicated that cracks initially appeared at the bottom of the upper flange and the lower flange edge near the loading section, then developed diagonally in the tension zone adjacent to the loading section and the upper part of the web plate of the beam end. These cracks were mainly concentrated along both sides of the line connecting the loading point and the fulcrum. The measured shear force for cracking of the test beam segment was 1766 kN, while the design shear force was 962.6 kN. The ratio of the measured to the design value was 1.835, indicating that the novel T-beam exhibits excellent crack resistance. Furthermore, a finite element numerical model of the beam was developed. The results showed that the predicted strain distribution in the web plate under the cracking load agreed well with the measured results, providing a reference for the crack resistance assessment of the diagonal section of novel prestressed T-beams.