Abstract: To explore the dynamic response laws of high-speed railway subgrade crossing the ground fissure zone under the variation of groundwater level,a physical model test with a geometric scale of 1:20 was carried out. The transient dynamic responses of dynamic stress,acceleration,and displacement of high-speed railway subgrade under varying groundwater levels were studied,including cases with no groundwater,as well as groundwater differences of 5.0 m and 15.0 m between the hanging wall and footwall of ground fissure. The results show that the dynamic displacement,acceleration,and dynamic stress in the subgrade increase as the groundwater level difference increases,with a higher response observed in the hanging wall compared to the footwall. The increase of the groundwater level difference intensifies the differential settlement value of the hanging wall and footwall of the embankment layer near the ground fissure by 180%,and the surface layer of the foundation by 31%.The dynamic acceleration in the subgrade of the hanging wall and footwall of the ground fissure decreased by 84.5% to 87.8% along the depth direction,and the dynamic stress decreased by 85.3% to 96.3%,but its attenuation is less affected by the change of groundwater level. However,the influence depth of dynamic stress increases with the increase of groundwater level difference,with a lower influence depth of dynamic stress observed on the hanging wall compared to the footwall. The critical influence depth of dynamic stress of the subgrade in actual engineering construction is more than 14.6 m. Based on the effective vibration velocity method,the short-term dynamic stability of the subgrade under different groundwater level differences is good when the train speed in the ground fissure site is less than or equal to 250 km·h^-1,but the dynamic stability of the hanging wall is lower than that of the footwall in the ground fissure site,and the stability of the subgrade decreases with the increase of the groundwater level difference in the ground fissure site. The research results can provide a scientific basis and guidance for the theoretical analysis of dynamic response and disease prevention of high-speed railway subgrade crossing the weak zone of ground fissures.