Abstract: This study established a finite element model for low-velocity impact analysis of glass fiber-reinforced polymer (GFRP) composite T-joints using ABAQUS. The interfacial delamination behavior was simulated via the Cohesive Zone Model (CZM), and the model’s accuracy was validated through physical impact tests. A bidirectional framework integrating numerical simulation and experimental testing was developed to systematically analyze the influence of fiber layup angles on structural damage evolution and mechanical performance. The results indicate that numerical simulations of load-displacement response curves and macroscopic failure morphologies are in good agreement with those of the experimental data with an error of 6.69%, which verifies the reliability of the multiscale modeling approach. When the layup sequence is 45/45/0/90/0_2s, the impact resistance performance is optimal. Among them, the ±45° layers enhance the shear resistance and disperse the impact energy; the 0°/90° orthogonal layers can significantly improve the tensile and compressive strength, and effectively suppress energy concentration through synergistic effect. This work elucidates the mapping relationship between the fiber layup configurations and the impact-induced damage mechanisms, providing a theoretical basis for the anti-impact design and engineering application of T-joints in composite materials.