The　impact　head,　tip　leakage　vortex,　and　pressure　pulsation　during　start-up　can　cause　vibration　and　noise　in　the　pump,　and　affect　its　hydraulic　performance.　The　linear　speed　start-up　method　cannot　solve　the　impact　head　and　vibration　problems.　Therefore,　in　this　study,　a　mixed-flow　pump　was　investigated　to　explore　the　influence　of　different　speed　start-up　schemes　on　the　flow　field　and　to　optimize　them.　The　rated　speed　was　set　to　1634　r/min,　and　numerical　simulations　of　different　start-up　schemes　were　carried　out　using　the　standard　k-Ε　model.　Furthermore,　the　turbulent　kinetic　energy　distribution　of　the　inlet　and　outlet　sections　of　the　mixed-flow　pump　during　different　start-up　schemes　was　provided.　In　addition,　the　normalized　helicity　and　blade　surface　pressure　for　different　start-up　schemes　were　compared.　Finally,　an　evaluation　function　was　proposed　to　evaluate　the　stability　of　the　flow　field　during　start-up.　The　results　showed　that　the　evaluation　function　had　four　factors　related　to　speed　and　acceleration　during　start-up.　Factors　α　and　γ　were　obtained　based　on　the　acceleration　and　speed　at　0.2　s　and　0.42　s　during　start-up,　respectively.　Factor　β　was　affected　by　the　time　taken　to　reach　the　rated　speed.　Parameter　δ　was　determined　by　the　acceleration　of　the　period　before　reaching　the　rated　speed.　Based　on　the　evaluation　function,　a　theoretical　scientific　selection　of　speed　start-up　scheme　is　proposed　to　improve　the　stability　of　the　flow　field　in　the　pump　during　start-up.　©　2023