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Facing the rising pressure of global environment changing rapidly, energy crisis and energy saving, the technology needs of the bi-directional DC/DC converter (BDC) which has the advantages of high efficiency, small size, good dynamic performance and low cost are increasing. This paper analyzes the advantages and disadvantages of the traditional isolated bi-directional DC/DC converters, furthermore, an isolated, high efficiency, high power density LLC resonant bi-directional DC/DC converter with symmetrical topology is proposed. Through studying the calculation method of the LLC resonant circuit parameters, a 5kW, 580V/400V BDC prototype model is designed. The corresponding equivalent circuit model is established in the Cadence Pspice environment. Simulation results verify the correctness of the bi-directional DC/DC converter with symmetric topology and the calculation method of resonant circuit component parameters and show that the BDC can realize ZVS for the power switches on the resonance side and realize ZCS for the rectifier diodes on the rectifier side in the whole load range. The converter reduces loss and electromagnetic interference (EMI) and improves efficiency.