Steiner　minimal　tree　is　a　fundamental　model　in　VLSI　routing.　Further　considering　X-architecture,　the　presence　of　obstacles,　and　the　requirements　of　multilayer　routing,　this　paper　presented　an　efficient　algorithm　based　on　particle　swarm　optimization　for　constructing　the　multilayer　obstacle-avoiding　X-architecture　Steiner　minimal　tree.　Edge　transformation　was　designed　to　make　the　particles　have　the　greater　ability　to　change　the　topology　of　the　routing　tree　and　avoided　the　obstacles.　The　new　operators　combined　with　union-find　set　were　designed　to　prevent　the　generation　of　the　loops.　In　order　to　avoid　obstacle　and　discourage　the　generation　of　vias,　the　penalty　function　related　to　obstacle-avoiding　and　vias　was　proposed.　The　proposed　algorithm　finally　optimizes　the　total　cost　of　routing　tree　which　is　the　most　important　optimization　target　of　the　multilayer　routing.　The　experimental　results　show　that,　the　proposed　algorithm　is　effective　and　superior　to　state-of-the-art　multilayer　routing　algorithms　on　the　total　cost.　©,　2015,　Institute　of　Computing　Technology.　All　right　reserved.