Coalition　formation　is　a　key　topic　in　multi-agent　systems.　One　may　prefer　a　coalition　structure　that　maximizes　the　sum　of　the　values　of　the　coalitions,　but　often　the　number　of　coalition　structures　is　too　large　to　allow　exhaustive　search　for　the　optimal　one.　Furthermore,　finding　the　optimal　coalition　structure　is　NP-hard.　Thus　emerges　the　meaningful　problem:　when　practical　applications　can　present　required　real　bound　on　the　worst　case,　and　how　to　attain　this　demand　via　partial　search?　This　paper　reports　on　a　novel　algorithm　based　on　cardinality　structure:　the　bound　K≥2　can　be　attained　with　searching　of　those　coalition　structures　whose　cardinality　structure　is　in　the　CCS(n,　K).　Finally,　experiments　indicates　the　new　algorithm　is　obviously　better　than　existing　algorithms.　©2007　IEEE.