The invention relates to a method for increasing the loading capacity of a three-phase energy storage inverter system. The method is applied to the three-phase energy storage inverter system comprising an energy storage inverter, a power grid side relay, an off-grid relay and bypass relays. The output side of the energy storage inverter forms a power grid end after passing through the power grid side relay and is connected to a power grid; the output side of the energy storage inverter forms an off-grid end used for being connected with a load after passing through the off-grid relay; and thebypass relays are connected between the power grid end and the off-grid end. The method for increasing the loading capacity of the three-phase energy storage inverter system comprises the following steps: connecting the load after short circuiting two or three live wires at the off-grid end; in the presence of the power grid, closing the power grid side inverter and one phase of bypass relay corresponding to any one of the short-circuited live wires; and in the absence of the power grid, closing the off-grid relay, and controlling the corresponding inverter power module to perform current-sharing output according to the phase of the short-circuited live wire. According to the invention, the loading capacity of the three-phase energy storage inverter system can be improved, and the flexibility of off-grid end in load connection is improved.