Abstract: To study the safety influence of a newly built water supply tunnel on the existing railway subgrade, a three dimensional numerical model was established by Midas NX to simulate the shield construction, based on the Damaowu-Renhe water supply tunnel shield underneath the Xuan-Hang railway located in Hangzhou. The displacement of the existing railway subgrade was calculated and the effectivity of the sub-regional reinforcement(splitting grouting reinforcement area, high pressure jet grouting pile reinforcement area and compaction grouting reinforcement area) was studied. Results show that due to the reinforcement measures, the lateral displacement induced by the tunnel shield construction is small enough to be neglected. In the reinforced area, the deformation is mainly vertical settlement with the maximum value of 8.6mm; and the uplift is the main deformation outside the reinforced area which the maximum value is 17.0mm. The maximum displacement location changes with the shield excavation. The sub-regional reinforcement measures can reduce the existing railway subgrade deformation induced by the tunnel shield construction effectively, which insures the safety operation of the existing railway.