The invention relates to a weak-magnetic control method and device of a high-speed permanent-magnet generator. When the speed of turbulent-flow wind is suddenly increased, the voltage of a port at the side of an instantaneous ultra-speed machine of the high-speed permanent-magnet generator is increased sharply, and when the voltage of the port of a motor is higher than an allowable voltage of a port of a current transformer at the side of the motor, a constant-voltage control strategy is adopted so as to guarantee safety of the current transformer of the unit. The weak-magnetic control method and device have the advantages that safe operation of the high-speed permanent-magnet full-power unit under the ultra-speed working condition is realized.