Abstract: This paper aims to estimate and control the bone cutting depth of the surgical robot in real time. Firstly, a cutting depth estimation model based on acoustic signal is established, and the influencing factors of model parameters are analyzed. The influences of different cutting processes and motion parameters on the model parameters are reduced through verification experiments. Then, the cutting depth control principle and the stability of the surgical robot are analyzed, and a bone cutting depth control method for a surgical robot based on acoustic signal is proposed. FFT (fast Fourier transform) is used to extract the first harmonic amplitude of the tool rotation frequency from the cutting acoustic signal as the feedback, and the model parameters are adjusted online according to the robot motion parameters to estimate the bone cutting depth, and then the bone cutting depth of surgical robot is controlled through PID (proportional-integral-differential) controller. Finally, the proposed method is verified by experiments, and the estimation accuracy and the safety range are evaluated experimentally, and compared with other methods. The results show that the changes of the deformation or the bone density have little influence on the cutting depth control by the proposed method. For the pig spine with different fixation methods, the cutting depth can be maintained in an acceptable range. Within the milling depth range of 0∼0.5 mm, the signal linearity is high, and the independent linearity rate can reach 8.812% F.S. (full scale). The proposed method can be used to improve the safety of the bone cutting operation for the surgical robot.