An optically enabled z-axis micro-disk inertia sensor is presented, which consists of a disk-shaped proof mass integrated on top of an optical waveguide. Numerical simulations show that the optical power of laser beam propagating in a narrow silicon nitride (Si₃N₄) waveguide located under the disk is attenuated in response to the vertical movement of the micro-disk. The high leakage power of the TM mode can effectively be used to detect a dynamic range of 1 g ? 10 g (g=9.8 m/s²). At lest, the waveguide is kept at a nominal gap of 1 ?m from the proof mass. It is adiabatically tapered to a narrow dimension of W×H = 350×220 nm² in a region where the optical mode is intended to interact with the proof mass. Furthermore, the bottom cladding is completely etched away to suspend the waveguide and improve the optical interaction with the proof mass. The proposed optical inertia sensor has a high sensitivity of 3 dB/g when a 50 μm-long waveguide is used (normalized sensitivity 0.5 dB/μm²) for the vertical movement detection.