The　relationship　among　SU,　detection　threshold,　bandwidth,　spectrum　utilization　and　secondary　throughput　in　cognitive　radio　networks　was　analyzed,　which　indicates　the　lower　false　alarm　probability,　higher　spectrum　utilization　and　larger　secondary　throughput　with　less　SU　in　C-CSS(censoring　based　cooperative　spectrum　sensing),　besides,　the　required　detection　threshold　for　maximizing　the　secondary　throughput　different　with　the　traditional　CSS　under　given　SU　number　and　the　objective　demand.　Based　on　the　NP　criticism,　an　optimal　cooperative　spectrum　sensing　algorithm　for　maximizing　the　secondary　throughput　was　proposed　by　solving　the　mathematic　model　to　obtain　the　optimal　party　of　SU　and　detection　threshold.　Theoretical　analysis　and　simulation　results　show　that　the　maximized　secondary　throughput　achieved　by　the　proposed　optimal　algorithm,　while　maintaining　the　given　detection　probability.