The　control　valve　of　a　diesel　unit　pump　fuel　system　adjusts　the　pressure　of　the　high-pressure　fuel　line　through　rapid　opening　to　achieve　fuel　cut-off　control.　Previous　research　shows　that　the　inner　flow　of　the　control　valve　is　a　dynamic　cavitation　flow　process,　and　both　the　inlet/outlet　pressures　and　valve　lift　have　great　influence　on　this　process.　However,　the　effect　of　the　valve　needle　speed　on　the　flow　characteristics　is　not　clear.　This　study　presents　an　investigation　of　the　effect　of　the　valve　needle　speed　on　the　flow　characteristics　within　the　control　valve　region　during　the　fuel　offloading　process　of　a　diesel　unit　pump　fuel　system　based　on　a　homogenous　two-phase　unsteady　flow　numerical　model.　The　results　show　that　under　the　condition　of　same　inlet/outlet　pressures,　as　the　valve　needle　speed　increases,　the　cavitation　intensities　of　both　the　conical　region　and　the　conical　downstream　region　are　weakened.　The　effects　of　the　valve　needle　speed　on　the　mass　flow　rate　under　the　condition　of　small　valve　needle　opening　can　be　ignored;　under　the　condition　of　large　valve　needle　opening,　the　higher　the　valve　needle　speed　is,　the　greater　the　mass　flow　rate　is.