In　allusion　to　the　deficiencies　existing　in　current　structural　optimization　algorithm　of　excavator　boom　such　as　the　inefficiency　in　expressing　and　handling　the　constraints,　the　insufficiency　in　adopting　the　task　knowledge　to　direct　constraint　handling,　and　the　difficulty　in　obtaining　and　adopting　the　optimal　process　knowledge,　a　new　method　of　the　constraints　expression　and　handling　based　on　cultural　algorithm　for　excavator　boom　structural　optimization　is　put　forward.　The　mechanism　of　hierarchical　constraints　expression　and　handing　is　established　to　improve　the　efficiency　of　the　constraint　handling　in　the　optimal　process　with　the　cultural　algorithm　as　frame　and　the　task　knowledge　as　guide.　And　the　hierarchical　topographical　knowledge　is　formed　to　express　tacit　knowledge　in　the　population　space.　Then　the　process　of　constraints　expressing　and　handling　as　well　as　its　interaction　with　the　knowledge　base　is　discussed　under　the　direction　of　dual　evolution　in　cultural　algorithm　while　the　aim　of　acquisition,　expression　and　handling　for　tacit　constraints　knowledge　in　optimal　process　is　realized.　Finally,　structural　optimization　of　an　excavator　boom　is　taken　as　an　example　to　demonstrate　the　effectiveness　of　this　method.　©　(2012)　Trans　Tech　Publications.