Due　to　the　high　water　pressure　at　the　bottom　of　the　tunnel,　when　drainage　system　is　not　well　designed,　railway　ballast　bed　may　suffer　from　diseases　such　as　contamination,　mud　pumping,　excessive　settlement　and　so　on.　Poor　drainage　will　significantly　reduce　the　performance　and　durability　of　ballast　bed.　In　this　paper,　a　novel　conceptual　drainage　and　water　pressure　reduction　system　at　the　bottom　of　railway　tunnel　is　proposed.　The　proposed　bottom　drainage　system　includes　a　transverse　catchment　system,　a　longitudinal　water　conducting　system　and　a　bottom-to-up　water　drainage　system.　A　series　numerical　analyses　were　carried　out　to　validate　the　performance　of　the　proposed　drainage　system.　Results　show　that　the　proposed　drainage　and　pressure　reduction　system　can　effectively　discharge　the　water　at　the　bottom　of　the　railway　tunnel　and　reduce　the　water　pressure.　Factors　that　influence　the　performance　of　the　proposed　drainage　system　are　also　discussed　by　parametric　studies.　The　permeability　of　the　surrounding　rock,　the　initial　support　and　the　secondary　lining　invert　have　great　influences　on　the　external　water　pressure.　The　groundwater　level　that　influences　the　water　pressure　reduction　effect　are　also　discussed.