In recent years, DC microgrid cluster has attracted attention for its higher permeability, stronger stability, better energy efficiency and so on. In this paper, a fully distributed optimal strategy is proposed to achieve the consistency of incremental cost, which is about generation cost and carbon emission. Based on the distributed communication, the consensus algorithm calculates the objective function at the microgrid level and the cluster level respectively. The results change the droop control of each distributed generators (DG). Considering the influence of line resistance on the accuracy of power proportional sharing, a novel droop controller is designed. The simulation model is built on the MATLAB /Simulink to verify the feasibility of the proposed control strategy.