In　cooperative　spectrum　sensing,　more　secondary　user　makes　more　opportunity　for　detecting　the　vacant　spectrums,　which　resulting　the　spectrum　utilization　improved,　however　much　bandwidth　would　be　occupied　for　sending　the　local　observation　results,　inducing　the　reduced　secondary　throughput.　In　this　paper,　an　adaptive　algorithm　for　selecting　detection　threshold　was　proposed,　where　the　maximized　secondary　throughput　can　always　be　achieved　while　assuring　sufficient　protection　to　primary　user,　regardless　of　the　number　of　sensing　users　in　cognitive　radio　networks.　Theoretical　analysis　and　simulation　results　validate　the　proposed　scheme.　©　2011　The　Journal　of　China　Universities　of　Posts　and　Telecommunications.