In this paper, an autonomous control method for ESS bi-directional DC/DC converter (BDCs) in DC micro-grid is proposed to solve the problems of difficulty in controlling the BDC converter of the ESS energy storage system (ESS) and the influence of constant power load instability during grid-connection, islanding-mode switching operation of DC micro-grid. In order to realize the smooth switching of various operation modes of DC microgrid. Firstly, the method adopts a completely decentralized control architecture to reduce the dependence of the control system on communication and improve the reliability of the system. Secondly, V2-P droop control is adopted to unify the bus voltage regulation and power regulation into one control structure, so as to avoid the design of switching monitoring mechanism and improve the stability of the system. In addition, V2-P droop control can eliminate the unstable influence of constant power load (CPLs). Finally, the experimental results show that the proposed method can achieve rapid and stable changes in the voltage and power distribution of DC microgrid during mode switching, and can also achieve good voltage regulation and power distribution in the steady-state mode.