Abstract: A robust H_∞ control strategy based on mixed sensitivity is proposed to improve the low-frequency characteristics of the flexible Hexapod vibration isolation system driven by voice coil motors. A stable low-order controller is obtained by a fixed-structure fast solver based on a non-smooth optimization algorithm for solving the implementation problem of high-order complex controllers by conventional methods. Results of simulation and experiment in frequency and time domains show that the proposed control strategy can effectively reduce the system corner frequency and improve the vibration attenuation rate at low frequencies. The isolation effect of the flexible Hexapod vibration isolation system at low frequencies is significantly enhanced.