Aiming at the low flutter stability limit of boring bar with high length-diameter ratio in deep hole boring finishing,which leads to flutter easily,an adaptive damping boring bar system was designed.By adjusting the axial compression of the O-ring spring,the natural frequency of the damper with additional mass damping was tuned to maximize its dynamic stiffness and adapt to a wide range of length-diameter ratio.Then,the frequency response function of boring bar was automatically measured by electromagnetic exciter and non-contact capacitive displacement sensor,and the natural frequency of additional shock absorber was adaptively tuned by compressing O-ring.Finally,the negative real part of the frequency response function of the boring bar was minimized to improve the chatter-free cutting depth maximatily.The results show that the real part of the frequency response function of boring bar is reduced from -15.17 μm/N to -0.24 μm/N,which means that the dynamic stiffness is increased by 63.2 times,and the surface roughness is obviously improved.The system can cover a wide range of length-diameter ratio of boring bar,and meet various practical installation requirements.