Under the long-term effect of disasters such as rainstorms and floods, the soil layer around the subway station may be affected by internal erosion, threatening the structural safety of urban subway stations. Exploring the influence of internal erosion on the subway station structure is crucial for ensuring the sustained normal operation and maintenance of existing subway stations. Isotropic consolidation and triaxial compression tests were conducted on gap-graded sand, with adjustments of the fine particle content, to explore the variations in physical and mechanical properties caused by internal erosion. Results indicate that internal erosion alters the stress-strain relationship of gap-graded sand, increasing compressibility, decreasing soil shear strength, and weakening dilatancy. DP Cap model parameters for eroded sand were determined based on the test results. ABAQUS was employed for numerical simulation analysis, and the deformation and internal force response of subway station and site soil under internal erosion disaster was analyzed. Results reveal that the internal erosion disasters at the top and sides of subway stations have minimal effects, while bottom-side erosion causes significant settlement and internal force changes in station structures, which deserves enough attention.