This article aims to monitor and control the vertebral lamina′s milling depth of the orthopedic robot in real-time. First, based on the milling cutter′s geometric structure and the lamina′s forced vibration equation, the vertebral lamina milling process is modeled and analyzed. An acoustic signal-based monitoring method of milling depth is proposed. Then, a bone milling acoustic signal processing method based on the fast Fourier transform accurately extracts the harmonic amplitude whose frequency is an integer time of the surgery power device′s spindle rotation frequency when the frequency changes. The harmonic amplitude is used as a feedback signal. The robot′s planned axial feed rate is corrected based on the proportional-differential controller with a dead zone to control the milling depth. Finally, milling test experiments and milling depth control experiments are implemented on some artificial bone block based on a threedegree-of-freedom Cartesian robot system. Experimental results show that based on the milling acoustic signal′s harmonic amplitude, the milling depth is monitored with a resolution of 0. 1 mm within the safe measurement range of the milling depth of 0~ 1. 2 mm. Therefore, the method can effectively control the vertebral lamina′s milling depth during bone surface deformation and displacement. The proposed method can improve the accuracy and safety of the laminar milling operation of the orthopedic robot.