The invention discloses a standby power automatic switching method suitable for a distributed new energy grid, includes the following steps: (1) After issuing 2DL trip, rapidly detecting frequency difference and voltage phase difference between incoming voltage U and bus residual voltage U; 2) after that QF2 trips, if the fast switch is not successful, the residual voltage UMY of the working bus enters an unsafe area, and the switch is not allowed at this time; When the UMY coincides with the power supply voltage US for the first time, the main contact of the 3DL is closed, that is, thecapture synchronization is switched; Backup power switching device real-time calculates voltage phase angle difference and frequency difference between U and U., When U is ahead U is set, if the frequency difference does not exceed the set frequency difference, a closing pulse is generated; (3) When the capture synchronization switching is not successful, switch to residual voltageswitching. In the complex multi-power supply system realized by the invention, the short-circuit current in the complex and changeable topology structure in the network can quickly remove the fault, and the huge impulse current and the impulse voltage can be avoided to damage the automatic device.