Coalition　formation　is　a　key　topic　in　multi-agent　system.　However,　finding　the　optimal　coalition　structure　is　NP-complete.　Sandholm　and　Larson　et　al.　showed　that　it　was　necessary　and　sufficient　to　search　the　lowest　two　levels　of　the　coalition　structure　graph　in　order　to　establish　a　worst-case　bound　k.　How　to　do　further　search　after　the　lowest　two　levels　of　the　coalition　structure　graph　is　a　problem　which　hasn＇t　been　resolved　well　for　a　long　time.　In　actual　problem　such　as　task　assignment,　the　different　coalitions　have　the　characteristics　of　the　same　cardinality　and　same　value,　or　the　value　of　two　coalitions　with　the　same　cardinality　differs　a　bit.　This　paper　studies　the　problem　about　the　optimal　cardinality　structure　generation,　analyzes　the　grouping　thought　of　cardinality　structures　and　presents　a　new　anytime　algorithm　of　coalition　structure　generation.　The　algorithm　gives　further　search　that　can　decrease　bound　to　2.　After　the　minimal　search,　the　complement　search　from　the　bottom　to　top　in　the　process　is　also　discussed　that　declines　bound　from　2　to　1.　It　is　obviously　better　than　Sandholm　et　al.　and　Dang　et　al.＇　s　in　the　searching　number　of　cardinality　structure　and　coalition　structure,　or　attaining　bound,　which　is　a　important　progress　in　the　problem　of　coalition　structure　generation　based　on　cardinality　structure.