Abstract: In conventional cooperative NOMA (CNOMA) system, more power is allocated to weak users, and the power allocated to strong users is less than half of the total power. Meanwhile, strong users need to act as relays in cooperative communication. Above power allocation strategy will bring some burden to strong users. In order to balance the performance of strong and weak users in CNOMA system, a new power allocation strategy based on relay communication and simultaneous wireless information and power transfer (SWIPT) is proposed in this paper. Energy harvesting equipment is used to collect energy. The optimal power splitting factor of SWIPT and the closed expression of the system outage probability are derived through maximizing the sum rate. Considering the nature of the optimization problem, a monotonic optimization algorithm is proposed to solve the power splitting factor of SWIPT under the condition of the fixed power allocation. Simulation results show that without losing the performance of weak users, the outage probability of strong users is improved compared with conventional power allocation strategy, and the overall sum-rate increases by nearly 20% compared with conventional power allocation strategy in CNOMA system.