Abstract: DC distribution networks have become the development trend due to advantages of large power supply capacity, small loss and high power quality. However, the overload capacity of the converter is poor and the discharging current of the converter equivalent capacitor is large when a DC fault occurs, which puts forward high requirements for the rapidity and selectivity of the protection. In addition, DC circuit breakers(DCCBs) may fail to trip due to its difficulty in breaking DC fault current, and the protection is still needed to identify and isolate fault even after the converter is locked to ensure the restart and recovery of the system. Therefore, the backup protection for the meshed DC distribution networks should be paid attention to. This paper proposes a backup protection scheme for the meshed DC distribution networks on the basis of the transient DCCB tripping. When the DCCB on one side of the fault line fails to trip, the characteristics of the reactor voltage change rates on the non-fault lines are analyzed, and the fault identification and isolation scheme based on the DC current second-order change rates are proposed. Secondly, considering high resistance fault and asynchronous tripping of DCCBs, the additional criterion and locking criterion based on the DC current first-order and second-order change rates are proposed, respectively. Finally, the effectiveness of the proposed scheme is verified with PSCAD/EMTDC simulations, indicating that the scheme needs no communication and is unaffected by transition resistance and AC side faults, which can start quickly after the DCCB tripping and provide effective backup protection for the meshed DC distribution networks.