Because　introducing　the　trust　degree　as　the　basis　of　component　service　selection　can　make　composite　services　to　be　scheduled　and　executed　around　the　trust　degree　of　services,　thus　higher　trust　degree　services　can　join　into　service　composition　and　the　trustiness　of　composite　service　can　be　improved,　trust　is　introduced　into　service　composition　and　the　component　service　selection　problem　of　trust　aware　in　service　composition　is　discussed.　The　mathematic　model　of　the　selection　problem　is　proposed　and　the　problem　is　reduced　to　a　minimum　cost　set　cover　problem.　The　directed　acyclic　graph　(DAG)　presentation　of　the　selection　problem　is　established　and　the　ant　colony　system　based　selection　algorithm　is　designed.　The　analysis　of　the　experimental　results　indicate　the　selection　algorithm　has　good　performance.