Coalition　formation　is　a　key　topic　in　multi-agents　system,　however,　finding　the　optimal　coalition　structure　is　NP-complete.　Sandholm　and　Larson　et　al.　showed　that　it　is　necessary　and　sufficient　to　search　the　lowest　two　levels　of　the　coalition　structure　graph　in　order　to　establish　a　worst-case　bound　k.　When　practical　applications　can　present　required　real　bound　in　the　worst　case,　how　to　do　a　further　minimal　search　to　find　a　coalition　structure　which　value　can　be　guaranteed　to　be　apart　from　optimal　coalition　structure　value　mutually　in　a　given　bound.　It　is　a　problem　that　deserves　to　study　and　hasn＇t　been　solved　for　a　long　time.　This　paper　analyzes　the　different　method　of　grouping　influence　on　the　number　of　cardinality　structures,　and　presents　a　new　grouping　method　and　a　new　algorithm　of　coalition　structure　generation　for　the　given　bound　in　the　worse　case,　decreases　greatly　the　demanded　searching　the　number　of　cardinality　structure　or　coalition　structure.