As　the　basic　model　for　very　large　scale　integration　routing,　the　Steiner　minimal　tree　(SMT)　can　be　used　in　various　practical　problems,　such　as　wire　length　optimization,　congestion,　and　time　delay　estimation.　In　this　paper,　an　effective　algorithm　based　on　particle　swarm　optimization　is　presented　to　construct　a　multilayer　obstacle-avoiding　X-architecture　SMT　(ML-OAXSMT).　First,　a　pretreatment　strategy　is　presented　to　reduce　the　total　number　of　judgments　for　the　routing　conditions　around　obstacles　and　vias.　Second,　an　edge　transformation　strategy　is　employed　to　make　the　particles　have　the　ability　to　bypass　the　obstacles　while　the　union-find　partition　is　used　to　prevent　invalid　solutions.　Third,　according　to　the　feature　of　ML-OAXSMT　problem,　we　design　an　edge-vertex　encoding　strategy,　which　has　the　advantage　of　simple　and　effective.　Moreover,　a　penalty　mechanism　is　proposed　to　help　the　particle　bypass　the　obstacles,　and　reduce　the　generation　of　via　at　the　same　time.　Experimental　results　show　that　our　algorithm　from　a　global　perspective　of　multilayer　structure　can　achieve　the　best　solution　quality　among　the　existing　algorithms.　Finally,　to　our　best　knowledge,　we　redefine　the　edge　cost　and　then　construct　the　obstacle-avoiding　preferred　direction　X-architecture　Steiner　tree,　which　is　the　first　work　to　address　this　problem　and　can　offer　the　theory　supports　for　chip　design　based　on　non-Manhattan　architecture.　©　2013　IEEE.