Diamond turning based on fast tool servo (FTS) is considered to be a very potential ultra-precision machining technology 〖JP〗for fabricating the optical free form surfaces. The current three degrees of freedom FTS has the problem of motion coupling, resulting it is difficult to plan tool path and the tool life is affected.A novel three degrees of freedom tandem FTS was presented.By the movementseries on X, Y, Z directions, the difficulty of motion decoupling in X, Y, Z directions was avoided.Analyzing the requirements of three degrees of freedom FTS should have, the cross-sectional shape, material and sizes of the flexible hinge were determined.The finite element simulation of the three degrees of freedom tandem FTS device was made by using ANSYS.It is shown that the maximum stresses at X, Y, Z directions of the flexible hinge are much smaller than the material allowable stress,the resonance frequencies of the first six vibration modes are much higher than the working frequency.The results show that the stresses and the resonance frequencies of the device meet the application requirements.