Abstract: In this paper， a cooperative non-orthogonal multiple access system using simultaneous wireless information and power transfer is investigated in an underlay cognitive radio network. In our proposed system， a two-stage relay selection strategy is proposed. The relay nodes take power splitting protocol to harvest the transmission power and use collected energy to decode and forward the users’ message. In realistic conditions， ideal successive interference cancellation can not be performed by the relay and secondary destination. The outage probability expression for each secondary user is derived under the conditions of the interference temperature constraint and non-ideal successive interference cancellation. The simulation results are provided to verify the correctness of our analytical results. Also， the influences of system parameters （the maximum transmit power at $\mathrm{S}$， interference temperature constraint， power allocation factor， etc.） on secondary users’ outage performance are analyzed quantitatively， and the relevant simulation results demonstrate that the outage performance of our proposed strategy is better than the partial relay selection strategy under the same parameters setting.