In the engineering test of an electric-optic turret, it was found the systems inherent frequencies were distinctly lower than the designed ones.To explain this phenomenon, the stiffness coupling between the electric-optic turret and the vibration isolator was analyzed.Further more, a new design method of vibration reduction based on stiffness matching was proposed, and was applied in the improved design of the turret.The subsequent tests proved the effectiveness of this method.