Cooperative technology could improve communication reliability by exploiting transmit diversity. However, the issue of imperfect frequency and timing synchronization makes it a challenge in practice. In this paper, we propose a novel cooperative communication scheme based on full space-time network code (FSTNC), which can maintain a stable network throughput and overcome the imperfect frequency and timing synchronization. Compared with space-time network code (STNC), FSTNC considers the relay cooperation and transmission order, and thus it further enhances the system reliability and efficiency. To verify the performance of the proposed scheme and reveal its advantage, we derive the exact symbol-error rate (SER) expressions for arbitrary order M-ary Phase Shift Keying (M-PSK) modulation and verify by simulations. The simulation results show that the proposed FSTNC scheme outperforms the conventional STNC scheme in terms of the SER performance. The advantage is more distinct when the relay transmission order is taken into consideration.