The　solenoid　valve　in　the　unit　pump　system　(UPS)　controls　the　pressure　buildup　within　the　high-pressure　fuel　line.　When　it　is　opened,　the　high-pressure　fuel　flows　with　high　velocity　from　the　narrow　cross-section　into　the　low-pressure　fuel　line.　During　its　operation,　the　flow　in　the　field　of　solenoid　valve　is　quite　complex　and　affects　the　performance　of　UPS.　This　study　presents　a　visualization　test　method　of　the　solenoid　valve　of　the　UPS.　For　the　optical　observation,　a　glass　window　was　incorporated　into　the　pump.　The　bubbles　induced　by　the　cavitation　under　various　operating　conditions　were　observed　by　a　high-speed　camera.　All　color　images　were　transformed　into　the　gray　pictures.　Simulation　was　conducted　on　the　basis　of　the　test　data　such　as　the　pressure　and　the　displacement　of　valve　core.　The　test　results　show　that　cavitation　phenomenon　occurs　during　the　opening　process　of　control　valve.　The　simulated　results　of　cavitation　regulation　in　control　valve　agree　well　with　the　experimental　results.　Simulation　results　show　that　cavitations　in　the　control　valve　mainly　occur　at　three　positions,　they　are,　the　cone　angle　of　valve　port,　the　downstream　of　cone　angle　and　the　clearance　between　the　valve　stop　and　the　core.　The　reasons　of　cavitation　generated　in　those　positions　were　discussed　based　on　the　simulation　results　of　the　flow　and　the　pressure　fields.