Abstract: In order to improve the transmission efficiency of quadrature modulated cooperative diversity system, the joint network coding and quadrature modulated scheme for cooperative hybrid automatic repeat request (NC-QM-HARQ) was proposed. By introducing network coding in the retransmission, this scheme could retransmit more information at the same time, thus the retransmission time was saved, resulting in the improvement of the throughput. Furthermore, based on the system’s Markov state transition model, the frame error rate (FER) and delay performance in the modulation of M-ary pulse amplitude modulation (PAM)were investigated, therefore the closed approximate solution of the throughput was acquired. Simulation results show that, the proposed scheme outperforms the traditional quadrature modulated cooperative diversity system HARQ scheme by a throughput gain of approximate 8% in the following scenes: 2PAM modulation at 5dB SNR, 4PAM at 10dB and 8PAM at 15dB.