A vanadium cell SOC estimation method based on charging/discharging energy efficiency is characterized in that the cell working is divided into a charging process and a discharging process, and correspondingly, the cell energy is divided into the charging-side energy and the discharging-side energy; the charging-side energy is mapped into the discharging-side energy by the charging/discharging efficiency of a cell under different currents to obtain the static state of charge(SOC) of the cell; the SOC of the cell are estimated under the loads by taking the reference load discharging capacity as the reference energy and according to the SOC and the discharging capacities of the cell under different loads. The method comprises the concrete steps of (1) adopting different currents to charge the cell respectively to obtain the efficiencies of the cell under different currents to thereby obtain the SOC of the cell; (2) adopting different loads to discharge the cell to obtain the function relationships of different load releasable energy relative to a reference load to thereby obtain the SOC of the cell.