Aiming at the throughput maximization problem of D2D-NOMA system under the condition of imperfect successive interference cancellation， a D2D-NOMA system throughput maximization algorithm based on imperfect SIC is proposed. Firstly, under the constraints of service quality and maximum transmission power of cellular users and D2D users, an optimization model with the goal of maximizing the throughput of D2D-NOMA system is established by considering the imperfect SIC condition. Then the model is converted into a Markov decision process with throughput as reward. A power allocation algorithm is designed using the TD3 algorithm to maximize the system throughput. The simulation results show that compared with the DDPG algorithm, the genetic algorithm and the random power allocation algorithm, the proposed algorithm improves the throughput of D2D-NOMA system under imperfect SIC by 14%, 25% and 40%, respectively, and also shows better convergence and fairness.