Printed　circuit　board　(PCB)　automatic　routing　is　a　multi-objective　optimization　problem　that　involves　higher　routability,　shorter　wire　length,　less　via　count,　and　so　on.　Some　algorithms　have　been　proposed　for　PCB　automatic　routing.　However,　existing　methods　cannot　meet　the　various　electrical　constraints　in　industry.　In　this　work,　we　propose　an　optimized　3D　Astar　algorithm　which　takes　real　constraints　into　account　for　multi-layer　PCB　automatic　routing.　Our　3D　Astar　algorithm　extends　the　search　dimension　of　traditional　Astar　algorithm　to　3D　and　improve　the　distance　function.　To　verify　the　performance　of　the　proposed　algorithm,　experiments　are　carried　out　on　the　benchmark　based　on　real　PCB　designs.　Experimental　results　show　that　our　proposed　algorithm　achieves　more　than　95%　routability　and　has　a　significant　improvement　in　terms　of　via　count　compared　with　traditional　3D　Astar　algorithm.　©　2021　IEEE.