In this paper, an ultra-sensitive nano-displacement sensing system consisting of an all-dielectric and mechanically tunable metamaterial has been proposed. The proposed sensor takes benefits from highly sensitive Fano resonance peaks as a result of the asymmetrical topology of the metamaterial. Simulation results demonstrate that perfect Fano resonance peaks with ultra-narrow bandwidths are achievable in the reflection spectrum of the proposed metamaterial which can provide excellent sensing characteristics. Based on the simulations performed using the frequency domain solver, a sharp resonance peak of a spectral bandwidth around 0.9 nm can be attained at the wavelength of 651 nm. Furthermore, the optical sensitivity of 1.04 nm/nm obtained for the proposed micro device, to the best of our knowledge, is the highest has ever been reported. The simple fabrication process, high resolution, and relatively highly wide measurement range are among the other features of the proposed micro device which make it suitable for several applications ranging from tunable reflectors to high-accuracy inertial sensors.