Abstract: A sensing-based spectrum sharing network with multi-antenna is suggested, which is consisted of a single-input single-output (SISO) primary user (PU) pair and a multi-input single-output (MISO) secondary user (SU) pair. In proposed network model, PU sends message to the SU when PU occupies the channel. So the SU calculates total interference power constraint by received PU message and adaptively adjusts its transmit power in order to avoid harmful interference to PU. If the licensed band is empty, the SU immediately occupies the channel with maximum transmitted power. Simultaneously, in order to maximize the system achievable rate, the optimal power allocation strategies among transmitter antennas are derived under the primary interference power constraint. Finally, the derived optimal power control policies are validated through simulations. The results show that, compared to the opportunistic spectrum access and sensing-based spectrum sharing, derived power control policies in suggested system model exhibits better performance.