Sample　deposition　based　on　micro-droplet　ejection　has　broad　application　prospects　in　the　field　of　biomedicine.　For　biological　cell　printing,　a　hybrid　pneumatic-electrohydrodynamic　(HPEHD)　micro-droplet　ejection　system　is　built　in　the　laboratory.　Strong　electric　field　is　established　by　applying　a　high　voltage　between　the　nozzle　and　a　collector　electrode.　A　solenoid　valve　is　opened　temporarily;　high　pressure　gas　enters　the　liquid　storage　chamber,　and　produces　pressure　pulse,　which　extrudes　the　liquid　slightly　from　the　nozzle.　The　liquid　is　further　deformed　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%)　containing　human　peripheral　blood　mononuclear　cells　(PBMC)　as　bioink,　single　droplet　per　ejection　is　realized,　and　the　droplet　size　is　reduced　by　50%　due　to　the　presence　of　the　electric　field.　Through　flow　cytometry　and　microscopic　photos,　the　effect　of　ejection　process　on　the　short-Term　viability　of　cells　is　shown　to　be　negligible,　suggesting　HPEHD　ejection　a　potential　technology　option　for　cell　printing.　©　2019　Association　for　Computing　Machinery.