Abstract: When the power allocation is performed in a hybrid system based on Non-Orthogonal Multiple Access (NOMA) and Cognitive Radio (CR) networks, the quality of service of the Primary Users (PUs) and the Secondary Users (SUs) needs to be considered simultaneously. The system that both the PUs and the SUs exist in one cell is considered in this paper. The SUs are allowed to access the system by means of NOMA, when the interference caused by the SUs to the PUs does not affect the normal communication of the PUs. The proposed power allocation method can maximize the number of the SUs who can access the system, while several parameters of the PUs are considered dynamically such as the number, channel conditions, transmission power and Signal to Interference plus Noise Ratio (SINR) threshold during normal communication. The maximum number of the accessible SUs will vary with these parameters. The simulation results show that the complexity of the proposed power allocation method and the FTPC method are the same, in the case where the number of the PUs and the SINR threshold of the PUs and the SUs are the same for both methods, and the proposed allocation method can make the maximum number of the SUs that can access the system more than half of the FTPC method.