The invention discloses a high-speed flexible rotor dynamic balance method. The method comprises the following steps of: firstly, establishing a finite element model of a rotor, obtaining 1-order to n-order mode values and an r-order critical rotating speed of the rotor from numerical simulation results, and taking the axial rotor position corresponding to the r-order maximum mode value as a reference position of the rotor; secondly, arranging two mutually vertical vibration transducers at the reference position, acquiring transient response of the rotor from the 0rpm uniform acceleration to the maximum rotating speed in the permitted range of the rotor to obtain mode damping of the rotor, stabilizing the rotor at the balanced rotating speed, acquiring stationary response of the rotor at the balanced rotating speed, and calculating sizes and azimuths of the rotor on n balanced planes which need adding correcting values; and finally, adding the correcting values on the rotor, acquiringthe transient response of the rotor during uniform acceleration, and checking whether the rotor reaches the required balance precision. The method has no risk of added trial mass, saves the balancingprocess of the added trial mass, simplifies the balancing step, and improves the balance efficiency and the balance precision.