Green　ammonia　production　system　driven　by　renewable　electricity　will　be　under　frequent　dynamic　operation　due　to　the　fluctuation　of　renewable　energy.　The　nonlinear　dynamic　model　of　a　green　ammonia　synthesis　system　is　developed　and　the　dynamic　responses　of　PEM　(proton　exchange　membrane)　electrolysis　subsystem,　PSA　(Pressure　swing　adsorption)　subsystem　and　ammonia　synthesis　subsystem　during　the　start-up　process　and　under　the　fluctuation　of　renewable　electrical　current　are　analyzed.　The　start-up　dynamic　results　show　that　the　hydrogen　production　rate　of　PEM　electrolysis　system　is　positively　correlated　to　the　current.　The　nitrogen　output　of　PSA　system　is　affected　by　the　adsorption　time,　adsorption　pressure,　bed　length,　and　air　velocity.　A　start-up　period　of　300　min　from　the　warmed-up　state　to　the　design　state　can　maintain　the　temperature　rise　rate　of　the　ammonia　synthesis　reactor　at　approximately　40　K/h.　The　dynamic　results　under　step　fluctuations　of　electrical　current　show　that　the　PEM　electrolysis　subsystem　and　the　PSA　subsystem　response　fast　compared　to　the　ammonia　synthesis　reactor　and　buffer　tanks.　Using　large　buffer　tanks　to　smooth　the　fluctuation　allows　the　system　to　slide　with　the　variation　of　renewable　current　to　some　extent,　resulting　in　a　higher　outlet　ammonia　fraction　when　the　current　increases.　Different　volume　ratios　of　the　hydrogen　tank　to　the　nitrogen　tank　volume　can　lead　to　different　variations　of　the　hydrogen/nitrogen　ratio.　PID　controllers　can　effectively　maintain　the　bed　temperatures,　hydrogen/　nitrogen　ratio,　and　pressure　of　the　ammonia　synthesis　reactor　at　their　set　points　despite　fluctuations　in　renewable　electrical　current.　Buffer　tanks　are　necessary　to　compensate　for　the　imbalance　between　the　flow　rate　fluctuation　caused　by　current　change　and　the　flow　rate　regulation　caused　by　PID　controllers.