An innovative design for a fast tool servo （FTS） system exhibiting high response frequency， high precision， and a high driving force was proposed herein. A flexible hinge fitted with a generalized conic line was applied to construct a novel flexible mechanism. The coupling error of the undesired movement direction of the flexible tool holder was decreased efficiently using a symmetrically arranged structure. Moreover， the kinematic characteristics of the mechanism were comprehensively modeled. Subsequently， based on an improved BP neural network， a multi-objective optimization design for the structural size of the flexible mechanism was performed. The stroke and natural frequency of the designed structure was analyzed to balance these two conflicting design objectives. The three-dimensional model of this device was established based on structural parameters obtained via optimization. Furthermore， a finite element analysis was performed. It is demonstrated that the algorithm affords a perfect optimization effect. The flexible mechanism designed via optimization could achieve advanced performances and was hence suitable for the FTS flexible mechanism. Finally， a prototype of the device was manufactured， and performance tests were conducted to verify the optimization design process. Experimental results show that the static and dynamic performances of the proposed device satisfy the design requirements. Its natural frequency exceeds 7.6 kHz， the nominal stroke is approximately 6.4 μm， the resolution is approximately 12 nm， and the following accuracy is approximately 0.3 μm. In addition， the experimental results verify the feasibility of the designed FTS system for ultraprecision machining.