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-e　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　alpha　and　gamma　were　obtained　based　on　the　acceleration　and　speed　at　0.2　s　and　0.42　s　during　start-up,　respectively.　Factor　beta　was　affected　by　the　time　taken　to　reach　the　rated　speed.　Parameter　delta　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.