Sample　deposition　based　on　micro-droplet　ejection　(MDE)　has　broad　application　prospects　in　the　field　of　biomedicine.　As　a　potential　technology　option　for　cell　printing,　a　hybrid　pneumatic-electrohydrodynamic　(HPEHD)　MDE　system　is　built　in　the　laboratory.　Strong　electric　field　is　established　by　applying　a　high　voltage　between　the　nozzle　and　a　collector　electrode.　The　pneumatic　actuation　is　realized　via　a　solenoid　valve　staying　outside　of　the　liquid　chamber.　The　solenoid　valve　is　set　in　conduction　for　a　short　period　of　time　Delta　t;　gas　of　high　pressure　P-0　enters　the　liquid　chamber,　and　produces　a　pressure　pulse,　which　extrudes　the　liquid　slightly　out　of　the　nozzle.　The　liquid　is　deformed　further　in　the　electric　field　into　a　cone　shape　(Taylor　cone),　and　then　the　end　of　the　Taylor　cone　breaks　to　form　a　micro-droplet.　The　ejection　process　is　studied　using　machine-vision　and　image　processing.　With　sodium　alginate　(1.0%)　as　bioink,　single　droplet　per　ejection　is　realized,　and　the　droplet　size　is　reduced　by　50%　due　to　the　presence　of　the　electric　field.　It　is　found　that　increasing　the　voltage　has　little　effect　on　the　size　of　droplets.　In　contrast,　increasing　source　pressure　P-0　or　increasing　Delta　t　the　conduction　time　of　the　solenoid　valve　can　change　the　volume　of　droplet　in　a　wider　range.