The　size　and　uniformity　of　micro-droplets　are　key　factors　influencing　the　quality　of　the　molded　part　by　microdroplet　ejecting　additive　manufacturing　technology.　In　this　paper,　a　piezo-actuated　micro-droplet　ejection　device　for　generating　uniform　micro-droplets　is　studied.　The　piezoelectric　material　drives　the　flexible　diaphragm　to　vibrate　and　pushes　the　liquid　out　of　the　nozzle　and　produces　micro-droplets.　The　amplitude　of　the　diaphragm　under　different　control　parameters　and　its　influence　on　the　size　and　uniformity　of　the　generated　micro-droplets　are　investigated　by　numerical　simulation　and　experiment.　The　results　indicate　that　the　amplitude　of　the　diaphragm　is　affected　by　the　driving　voltage　and　the　piezoelectric　frequency　and　the　experimental　value　of　the　diaphragm＇s　center　point　amplitude　is　less　than　that　of　the　theoretical　calculation　value　which　is　mainly　influenced　by　the　piezoelectric　frequency.　The　amplitude　of　the　diaphragm　will　change　the　pressure　inside　the　nozzle,　which　leads　to　the　varied　sizes　of　the　micro-droplet.　When　the　driving　voltage　is　constant,　the　diaphragm　has　the　maximum　amplitude　for　the　piezoelectric　frequency　at　10　Hz.　As　the　amplitude　of　the　diaphragm　increases,　droplets　can　be　generated　when　the　liquid　velocity　at　the　orifice　and　the　length　of　the　liquid　column　increase　to　a　critical　value.　As　the　amplitude　of　the　diaphragm　continues　to　increase　and　the　length　of　the　liquid　column　at　the　orifice　is　beyond　to　a　critical　value,　a　satellite　micro-droplet　is　formed.　When　the　amplitude　range　of　the　membrane　is　between　30　µm　and　42　µm,　micro-droplets　can　be　stably　formed　whose　uniformity　and　size　meet　the　demand　well,　and　the　minimum　generating　micro-droplets　size　is　339.8　µm.　The　maximum　change　rate　of　droplet　diameter　and　adjacent　two　droplets　are　0.29%　and　2.67%　respectively.　Results　are　benefit　to　promote　the　uniformity　of　micro-droplets　and　will　provide　a　reference　for　the　development　of　piezoelectric　droplet　ejection　devices.　©　2019,　Chinese　Journal　of　Theoretical　and　Applied　Mechanics　Press.　All　right　reserved.