Optimal　designing　of　the　water　distribution　network　is　a　multi-variable　optimization　problem.　Due　to　the　problem　of　the　water　distribution　network,　an　ant　colony　optimization　(ACO)　method　is　proposed　for　designing　the　network.　The　proposed　ACO　set　the　penalty　function　for　each　node　and　the　conversion　cost　of　the　water　distribution　network　for　goal　to　achieve　the　goal　of　optimal　designing.　During　the　searching　process,　the　ACO　directly　selects　the　value　from　the　combination　of　pipe　diameter.　The　ACO　is　able　to　avoid　the　emergence　of　the　pipeline　diameter　which　can　not　meet　the　engineering　requirements.　Comparing　with　other　optimal　methods,　the　ACO　has　the　good　global　searching　ability　and　a　broad　application　prospects.　©　2011　IEEE.