With multiple primary-user coexisting, a new dual-hop cognitive cooperative communication system is proposed and analyzed. In this proposed system, multiuser existed at the destination and the optimal channel coefficient scheme is adopted to improve the system performance. Moreover, the outage probability performance is investigated over Rayleigh fading channels and the exact closed-form expression is derived, then an asymptotic expression at high signal-to-noise for the outage probability is obtained too. Finally, simulation results are presented to verify that the system performance is improved with multiuser condition.