The　movement　of　needle　valve　in　the　common　rail　injector　determines　the　injection　and　atomization　effect　directly.　The　movement　rule　of　needle　valve　in　the　common　rail　injector　is　important　to　improve　the　structure　of　injector　and　the　atomization　effect.　A　high-pressure　common　rail　injector　simulation　system　was　built,　and　a　calculation　model　was　established　for　optimizing　the　flow　coefficients　in　two　stages　of　cavitation　and　non-cavitation　at　the　oil　inlet　and　outlet　holes　of　high　pressure　common　rail　injector　and　in　the　ball　valve　area.　The　movement　characteristics　of　needle　valve　in　the　common　rail　injector　are　studied　through　theoretical　analysis　and　experiments.　The　results　show　that　the　opening　process　of　needle　valve　can　be　divided　into　two　stages:　slow　opening　stage　and　fast　opening　stage.　Two　opening　stages　of　needle　valve　are　due　to　the　transfer　of　the　throttled　position.　However,　the　needle　valve　is　mainly　influenced　by　the　throttled　position,　so　the　closure　of　the　needle　valve　is　a　single-stage.　Rail　pressure　has　an　effect　on　the　second　fast　opening　stage,　but　not　on　the　slow　opening　stage　or　the　closing　process.　The　opening　process　speeds　up　with　the　rise　of　the　rail　pressure.　When　the　rail　pressure　reaches　to　a　certain　value,　the　fast　opening　stage　of　needle　valve　remains　unchanged.　©　2017,　Editorial　Board　of　Acta　Armamentarii.　All　right　reserved.