The　transient　response　characteristics　of　fuel　cells　are　crucial　for　their　utilization　and　performance　optimization.　Optimal　transient　response　characteristics　guarantee　that　fuel　cells　maintain　efficient　electrochemical　reactions　during　load　changes.　This,　in　turn,　enhances　the　overall　efficiency,　performance,　stability,　and　safety　of　the　system　while　preventing　voltage　dips　and　reverse-polarity　issues.　This　study,　premised　on　single-cell　experiments,　investigates　the　variations　in　transient　response　characteristics　and　the　factors　influencing　fuel　cells　by　administering　step　loads　at　four　gradients:　400,　800,　1,200,　and　1,600　mA·cm-2　(extreme　condition).　Furthermore,　a　two-dimensional　multiphase　fuel　cell　model　is　employed　to　simulate　the　mass-transfer　processes　within　the　gas　diffusion　layer　under　varying　inlet　pressures,　relative　humidities,　and　flow　rates.　This　simulation　aimed　to　elucidate　the　mechanisms　by　which　these　factors　influence　the　transient　response　characteristics　of　the　fuel　cell.　The　results　indicated　that　reverse　polarity　occurs　when　the　current　density　surpasses　1,200　mA·cm-2,　primarily　due　to　rapid　changes　in　load　conditions.　Modifying　the　intake　pressure　and　relative　humidity　can　alleviate　this　issue,　but　not　entirely　eliminate　the　reverse　polarity　problem.　However,　an　increase　in　the　initial　flow　rate　markedly　enhances　the　transient　response　characteristics　of　the　fuel　cell　and　prevents　reverse　polarity　at　1,600　mA·cm-2.　This　research　offers　a　theoretical　foundation　for　enhancing　the　transient　response　characteristics　of　fuel　cells　and　optimizing　load　application　methods　in　practical　scenarios.　©　2025　American　Society　of　Civil　Engineers.