Abstract: In the relay-based cooperative spectrum sensing, the cooperative spectrum sensing performance can be effectively improved by introducing relay’s cooperation. In order to save the system cost, we propose a censoring based cooperative spectrum sensing with best relay on the basis of the prior work. Only when the secondary user has detected the primary user’s signal and its reporting channel is destructively faded, it will apply for the cognitive relay’s cooperation. We analyzed the cooperative spectrum sensing performance from the point of detection performance and the achievable secondary throughput. Both the theoretical analysis and simulation results show that the improved detection performance can be obtained by the proposed scheme, and when assuring sufficient protection to the primary user, the achievable secondary throughput can also be improved by the proposed scheme.