An　analysis　has　been　conducted　on　the　hydraulic　bridge　of　the　water　hydraulic　servo　valve　with　annular　clearance　between　sleeve　and　spool　land　as　its　first　hydraulic　resistance.　Through　some　formula　deductions,　the　simplified　hydraulic　bridge　is　drawn　and　the　relationship　between　flapper　displacement　and　differential　pressure　of　spool　ends,　which　is　demonstrated　by　the　subsequent　simulation　works,　is　extracted.　By　the　CFD(computational　fluid　dynamics)　simulation,　firstly,　the　pressure　distributions　of　the　flapper　face　and　the　fore　end　face　of　the　nozzle　are　obtained.　Results　show　that　the　flapper　has　an　annular　area　where　the　existing　pressure　is　negative.　Secondly,　the　relationship　between　flapper　displacement　and　flow　force　acting　on　flapper　is　also　acquired,　which　is　much　beneficial　to　the　steady-state　and　dynamic　analysis　of　the　water　hydraulic　servo　valve.