This　paper　presents　an　investigation　of　the　hydraulic　flow　characteristics　of　a　solenoid　injector　in　a　common　rail　fuel　system.　We　analyze　the　inner　flow　characteristics　of　the　entire　operational　process.　Based　on　this　theoretical　analysis,　we　develop　a　numerical　model　of　a　solenoid　injector　by　using　commercial　MATLAB/Simulink　integrated　design　environments.　A　test　rig　is　also　set　up　to　examine　the　movement　of　the　injector　needle.　Results　show　that　two　stages　occur　during　the　opening　process.　These　two　stages　of　the　needle　are　determined　by　the　effective　flow　cross　section　that　yields　a　two-stage　performance　of　the　mass　flow　rate.　Furthermore,　the　injection　pressure　affects　the　needle　lift　but　high　injection　pressure　has　minimal　effects　on　the　needle　lift　as　the　pressure　reaches　a　threshold.　©　2021　Begell　House　Inc..　All　rights　reserved.