The invention relates to an instantaneous power-down rebooting method for a grid of a high-voltage frequency converter. In the method, when instantaneous power down of the grid occurs, the state of a motor is converted into a generator state by controlling PWM waveout of a power unit, so that energy is fed back to the power unit of the high-voltage frequency converter to maintain a capacitor voltage of the power unit of the high-voltage frequency converter; when the grid recovers, the generator state of the motor is converted into the motor state, and the rotational speed automatically rises to original set value. The high-voltage frequency converter is a voltage-source type phase-shifting frequency converter comprising series-connected multi-level power units, and adopts large-inertia blower load. The method can solve the problem of big fluctuation of high-voltage source system or instantaneous power-down protection caused by switching the high-voltage source system, realize the continuous and stable operation of high-voltage frequency converter and motor when instantaneous power down of the grid occurs and the automatic speed rise to the original set value when grid returns to normal.