By　taking　into　account　of　the　factors　including　CFG　composite　foundation,　train　load,　backfill　grouting,　grouting　pressure,　shield　tunnel　working　face　pressure　of　soil　compaitinent,　the　numerical　model　of　FLAC3D　is　established　in　terms　of　the　geological　and　hydrogeological　conditions,　and　the　whole　process　of　the　shield　tunnel　traversing　beneath　a　high-speed　railway＇s　subgrade　is　simulated,　thus　the　lateral　and　longitudinal　settlement　of　the　subgrade　surface　was　predicted.　The　results　show　that　the　maximum　settlement　on　the　subgrade　surface　amounts　to　6.88　mm,　and　the　maximum　settlement　grade　is　0.29　parts　per　thousand,　and　settlement　trough　with　unimodal　shape　is　comparatively　flat;　the　longitudinal　settlement　induced　by　excavation　of　the　twin　shield　tunnels　consists　of　6　stages,　and　the　maximum　longitudinal　settlement　grade　equals　to　0.27　parts　per　thousand.