Multi-constrained　optimal　routing　problem　and　disjoint　path　selection　are　NP-hard　problem.　The　conventional　single-path　and　single　constraint　routing　can　not　meet　people＇s　needs.　The　reliability　of　network　data　transmission　and　packet　loss　rate　can　be　decreased　when　the　route　or　the　transmission　fails.　To　solve　the　problems,　we　need　to　study　the　routing　path　selection　strategies.　This　paper　optimizes　the　routing　path　that　meets　the　QoS　constraints　under　the　SDN　pre　planning　routing,　and　proposes　a　routing　mechanism　that　can　solve　problems　in　polynomial　time.　Firstly,　the　paper　combined　with　Clustering　and　Gauss　algorithm　to　simulate　the　network　simulation,　obtain　the　initial　experimental　data.　It　can　reflect　the　network　status　more　accurately.　Secondly,　simplify　the　multi-objectives　based　on　the　AHP,　It　reduces　the　complexity　of　the　problem　and　meets　QoS　requirements.　Finally,　select　the　disjoint　communication　paths　and　backup　paths　with　the　heuristic　algorithms　in　order　to　balance　the　load　of　network　and　improve　the　transmission　reliability.　The　selection　mechanism　can　improve　the　efficiency　of　data　transmission,　and　the　survival　of　network　communication.