Flexible hinge is widely used in fast tool servo,the design of the flexible hinge is an important part in the design of fast tool servo.A flexible hinge’s parameter optimization design method based on genetic algorithm was proposed for the design of flexible hinge guiding mechanism in three degree-of-freedom tandem fast tool servo.Firstly,according to the kinematic characteristics of three degree-of-freedom fast tool servo,the dynamic model was established.Then,according to the requirements of the flexible hinge as the guide mechanism of three degree-of-freedom fast tool servo in precision machining,the objective function and the constraint condition of maximum stiffness of flexible hinge in three directions were established.Finally,genetic algorithms was used to optimize the design of flexible hinges,obtaining the optimal parameters.