The　issue　of　coalition　formation　problem　has　been　investigated　from　many　aspects.　However,　all　of　the　previous　work　just　take　the　capability　of　agent　into　account,　but　not　consider　those　factors,　such　as　the　time　that　agent　takes　to　achieve　a　task,　the　cost　of　employing　agent,　the　credit　standing　of　agent,　the　risk　that　the　task　sponsor　bears,　and　the　bias　of　task　sponsor　and　so　on.　So　we　originally　take　these　factors　into　account.　The　coalition　problem　in　this　paper　is　a　constrained　problem　including　a　great　deal　of　equality　constraints　and　inequality　constraints.　So　we　adopt　the　death　penalty　function　to　transform　it　to　an　unconstrained　one.　That　is　to　say,　it　becomes　a　single　objective　function.　Being　an　unconstrained　optimization　algorithm,　the　binary　particle　swarm　optimization　algorithm　is　adopted　to　address　this　problem.　To　improve　the　capability　of　global　searching　of　our　algorithm　and　convergent　rate　of　the　solutions,　we　divide　the　process　of　coalition　formation　into　two　stages　to　deal　with　respectively.　Simulations　show　that　our　algorithm　is　effective　and　feasible.　©　Springer-Verlag　Berlin　Heidelberg　2007.