Abstract: Compared with single DC microgrid, DC multi-microgrid improves the power supply efficiency, however, its complex topology increases the difficulty of fault detection. At the same time, the communication failure or data loss of DC multi-microgrid reduces the reliability of protection, and even leads to protection failure. In order to solve the problem of protection failure caused by communication faults and improve the protection reliability, a cooperative protection strategy based on power gradient considering communication faults is proposed. When the communication is normal, the remote power gradient differential protection can quickly and selectively remove the short-circuit faults; In case of communication failure, the power gradient differential protection is locked and the local power gradient protection is started. The two kinds of protections act together, which has the advantages of unit protection and non-unit protection without adding measuring devices. Compared with overcurrent or current differential protection, the cooperative protection strategy has faster fault detection speed and higher sensitivity, and is not affected by communication faults. Finally, simulation results show the effectiveness of the proposed strategy.