The invention relates to an energy storage converting control technology, and in particular relates to a control method for realizing passive off-network seamless switching by using an energy storage converter. The method comprises the following steps of: (1) determining that an energy conversion system PCS of an energy storage system is in a grid-connected state; (2) recording the Nth three-phase line voltage sampling value of a power grid, wherein N is a natural number; (3) determining the difference between the Nth three-phase line voltage sampling value of the power grid and the (N-M)th three-phase line voltage sampling value of the power grid; (4) judging whether the difference in the step (3) associated with any one phase of the three phases is greater than 15% of the maximum value of the rated voltage or not; (5) when a counter K is greater than or equal to 3, marking the passive off-network position; and (6) when the passive off-network position is marked, the energy conversion system PCS of the energy storage system enters into the off-network state. The method provided by the invention can be used for realizing seamless switching between the grid-connected network and an independently operated off-network for a micro-network, so that power supply is continuously supplied by voltage and frequency in the micro-network, and the load power supply reliability in the micro-network is improved.