The invention discloses an energy-carried cooperative CR-NOMA cooperative mode and a relay selection algorithm based on CR-NOMA, comprising: when relay assists two users for information transmission, if the main user is able to decode correctly, then, using all the collected energy to assist the cognitive user to transmit information at the next time slot; otherwise, using the NOMA to continue forwarding the information of the two users; for the multi-relay, proposing the relay selection strategy of the two stages, or solving the set of the correctly decoded relays first; then enabling that the energy remaining and the channel gain from the second jumped relay to the main user are maximized; and solving the closed solution to the interruption probability of the two users and the expression of the throughput. With the invention, while the performances of the main user are ensured, the performances of the sub-user can be increased further so that when the main user reaches the full gain, the cognitive user reaches three-order gain. The energy efficiency of the system is also raised.